1) Given binomials:
First binomial 7r - 5
Second binomial 5r + 8
2) To pass from 7r to 5r you have to subtract 2r, so the first term of the binomial to be subtracted is 2r
3) To pass form - 5 to + 8, you have fo subtract - 13
4) So the answer is 2r - 13, option b.
