G = 4V

G-30 = V (doesn't matter when the comparison is made Vicky is always 30 years younger than Grace).

Add 30 to both sides of second equation.

G = V+30

substitute second equation in first.

4V = V +30

subtract V from both sides

3V = 30

Vicky is 10 years old

Grace is therefore 40

G-30 = V (doesn't matter when the comparison is made Vicky is always 30 years younger than Grace).

Add 30 to both sides of second equation.

G = V+30

substitute second equation in first.

4V = V +30

subtract V from both sides

3V = 30

Vicky is 10 years old

Grace is therefore 40