Question

S=R-rR solve for R the answer is R=S/1-r i just don't know how toget there

Answer 1

Remember the distributive property, we are gong to reverse that
1R-rR=R(1-r)

we now have
S=R(1-r)
divide both sides by (1-r)
$\frac{s}{1-r} = R$

Answer 2

S = R - rR
Take out R as a common factor on the right hand side.
S = R(1 - r)
Now divide both sides by (1 - r), to get R by itself:
S/(1 - r) = R