Question

Solve 4a + 23 - 9a - 17 =21 . Show work

Answer 1

4a + 23 -9a - 17 = 21....simplify
-5a + 6 = 21
-5a = 21 - 6
-5a = 15
a = -15/5
a = -3 <==

Answer 2

A=3
 First you would collect the like terms 
-5a+21-6
Move constant to the right
-5a=21-6
Subtract the numbers
-5a=15
Divide both sides by -5 and there ya go