Question

How do I do this example 8(10a-4)+5a and 5a-12 are equivalent? Is she correct?

Answer 1

8(10a - 4) + 5a = 5a - 12
8(10a) - 8(4) + 5a = 5a - 12
80a - 32 + 5a = 5a - 12
80a + 5a - 32 = 5a - 12
85a - 32 = 5a - 12
-5a           -5a       
80a - 32 = -12
       +32    +32
       80a = 20
        80     80
           a = 1/4