You cannot solve this equation from the data provided. The equation is expressed incorrectly. This is clear because X (the unknown) represents two different things in the equation.

Your sum says that 10 mg is the same of an unknown quantity (X) of teaspoons.

You are then asserting that 1/8 of a teaspoon is also X mg.

This clearly cannot be the case.

It seems like what you are trying to express here is the following:

10mg = an unknown quantity (X) of teaspoons.

How many mg is the equivalent to 1/8 of a teaspoon?

You cannot provide an answer to this equation as there is insufficient data to do the calculation. You need to know how many teaspoons 10 mg is equivalent to in order to calculate the mg for 1/8 of a teaspoon.

What you can do is express the answer as a formula.

A formula is a syntactic object that can be given a semantic meaning. In other words, it's an expression where letters can be given meanings. In your example the syntactic letter of X has been given the semantic meaning of 'the equivalent teaspoons of 10 mg'.

Usage of formulas is part of logic in mathematics. They allow you to express unknowns and the relationships between them. In schools, this is usually taught when children get to around the age of 14.

It is a common stumbling block for many youngsters who are used to having to make calculations when all of the numbers in the sum are accounted for. But logic is one of the most useful forms of mathematics for later life.

Think of a recipe. If you want to make a batch of 20 cakes but your recipe is only for 13, you can use logical calculations to work out the measurements you will need to adjust the recipe.

Your sum says that 10 mg is the same of an unknown quantity (X) of teaspoons.

You are then asserting that 1/8 of a teaspoon is also X mg.

This clearly cannot be the case.

It seems like what you are trying to express here is the following:

10mg = an unknown quantity (X) of teaspoons.

How many mg is the equivalent to 1/8 of a teaspoon?

You cannot provide an answer to this equation as there is insufficient data to do the calculation. You need to know how many teaspoons 10 mg is equivalent to in order to calculate the mg for 1/8 of a teaspoon.

What you can do is express the answer as a formula.

A formula is a syntactic object that can be given a semantic meaning. In other words, it's an expression where letters can be given meanings. In your example the syntactic letter of X has been given the semantic meaning of 'the equivalent teaspoons of 10 mg'.

Usage of formulas is part of logic in mathematics. They allow you to express unknowns and the relationships between them. In schools, this is usually taught when children get to around the age of 14.

It is a common stumbling block for many youngsters who are used to having to make calculations when all of the numbers in the sum are accounted for. But logic is one of the most useful forms of mathematics for later life.

Think of a recipe. If you want to make a batch of 20 cakes but your recipe is only for 13, you can use logical calculations to work out the measurements you will need to adjust the recipe.