The difference of two numbers, a and b, is 21. The difference of 5 times a and two times b is 18. What are the values of a and b? A. 4,1 B. - 19,40 B. 20,1 C. 30,9 D. - 8,-29

A-b=21

5a-2b=18

We can use substitution here. Take the first equation and solve for A. (Picking this one because it's easy)

a = 21+b

Plugin to the second equation:5 (21+b) - 2b=18

Simplify: 105 + 5b - 2b = 18

Simplify: 105 + 3b = 18

Subtract both sides: 3b = 18-105

Simplify: 3b = - 87

Divide: b = - 29

Plug back into the first: a=21+b

a = 21 - 29

a = - 8

Option D