Short answer: C
Remark
Since b is all by itself in equation 2, Substitute it into equation 1.
2a + 3b = 5
b = a - 5 Put this result in equation 1. Be sure and use brackets.
2a + 3(a - 5) = 5 Remove the brackets.
2a + 3a - 15 = 5 Notice the -5 inside the brackets becomes - 15
Combine like terms on the left.
5a - 15 = 5 Add 15 to both sides
5a = 5 + 15
5a = 20 Divide by 5
a = 20/5
a = 4
So far, c is the only possible answer.
b = a - 5
b = 4 - 5
b = - 1
