Question

Why +1 was changed to +12 in the following problem?

Answer 1

because here they are multiplying 12 on both sides which gives

1*12=12

Answer 2

z-1/3 = 1 +z - 2/4

multiplying both sides by 12

so

12(z-1 / 3 ) = 12 [ 1 + (z - 2 / 4 )]

12(z-1 / 3) = 12 + 12(z - 2 / 4)