Question

What should be added to 8a to get 12a ? ​

Answer 1

Let me do step wise step. So here,
Solution,
8a+?=12a
Let, the required number be “x”
Now,
8a + x = 12a
or, x = 12a - 8a (8a was positive before but after coming on RHS it became positive)
or, x = 4a

∴ The required number (x) is 4a.