Proof:

Suppose:

a + b = c

This can also be written as:

4a - 3a + 4b - 3b = 4c - 3c

After reorganizing:

4a + 4b - 4c = 3a + 3b - 3c

Take the constants out of the brackets:

4 x (a+b-c) = 3 x (a+b-c)

Remove the same term left and right:

4 = 3

Hence proved.... :)