Its tricky on the computer,because I can't do it like it is on a page!But I'll do it for you.

Y2- y1 over x2-x1

4-2 over 1+3*

2 over 4

= 1 half.

*Remember the negative number is never happy and always tells the signs to change.But the positive number always tells the signs to stay the same.Also,think of it in terms of money,(you have and you owe,instead of normal addition and subtraction).I hope I helped you understand,as well as just doing the sum.

Y2- y1 over x2-x1

4-2 over 1+3*

2 over 4

= 1 half.

*Remember the negative number is never happy and always tells the signs to change.But the positive number always tells the signs to stay the same.Also,think of it in terms of money,(you have and you owe,instead of normal addition and subtraction).I hope I helped you understand,as well as just doing the sum.