Question

Justify each step.
7a + (4 + 12a) = 12a + 4

Answer 1

7a + 4 + 12a = 12a + 4 -> just open ( )
19a + 4 = 12a + 4 -> adding all the 'a' on the left side
now subtract 12a from both sides to get :
19a - 12a + 4 = 12a - 12a + 4
7a + 4 = 4
subtract 4 from both sides to get
7a + 4 -4 = 4 -4
7a = 0
obviously a = 0