This question seemingly has nothing to do with c++. In the future dont post math related questions in the programming forums.
As for your problem, what does the question ask you to do? Do you have to solve for the variable r?

1st) Read post 1, although if you PM, someone that knows a little math, he might help you.

2)

Let A = r+5(r-2)=28
Let B = 3(r+4)+5(r+2)=102
//Break down A
A = r+5(r-2) = 28
= r + 5r - 10 = 28 //distributive rule
= 6r - 10 = 20 //add like trms
= 6r = 20 + 10 //remember switching numbers to the opposite sides mean change its operatorion from + to minus, * to / and vice-versa
so, 6r = 20 + 10,
6r = 30
r = 30/6 = 15/3 = 5

//Break down of B
Let B = 3(r+4)+5(r+2)=102
B = 3r + 12 + 10r + 20 = 102 //Distributive property
= 3r + 10r + 12 + 20 = 102 // re-arrange like terms
= 13r + 32 = 102 //add like terms
= 13r = 102 - 32 //bring together like terms
= 13r = 70
= r = 70/13

Also with B: this B = 3r + 12 + 10r + 20 = 102 //Distributive property is completely wrong. I have no idea what you're trying to do here.
Look, if r(B)=70/13=5.38... (according to you) then if you substitute 'r' with 5.38... in the original formula, you should get 102; which you don't.

the answer to B is 10. But I'm not going to show the math here, because the OP needs to learn to do his/her own damn homework.

1st) Read post 1, although if you PM, someone that knows a little math, he might help you.

2)

Let A = r+5(r-2)=28
Let B = 3(r+4)+5(r+2)=102
//Break down A
A = r+5(r-2) = 28
= r + 5r - 10 = 28 //distributive rule
= 6r - 10 = 20 //add like trms
= 6r = 20 + 10 //remember switching numbers to the opposite sides mean change its operatorion from + to minus, * to / and vice-versa
so, 6r = 20 + 10,
6r = 30
r = 30/6 = 15/3 = 5

//Break down of B
Let B = 3(r+4)+5(r+2)=102
B = 3r + 12 + 10r + 20 = 102 //Distributive property
= 3r + 10r + 12 + 20 = 102 // re-arrange like terms
= 13r + 32 = 102 //add like terms
= 13r = 102 - 32 //bring together like terms
= 13r = 70
= r = 70/13

I thought you purposely gave him a dud answer so he would hand it in. Well done you had me fooled.