How do you go about rearranging equations where the required subject appears on both sides? Such as making x the subject of 7x + a = 3x + b.

To rearrange any equation, you must always do the same to both sides.
If you take a number from one side, you must also take it from the other. If you divide a side by one number you must divide the other by the same number (and this applies to the whole of both sides, not just part of the side).

7x + a = 3x + b, make x the subject:
Begin by collecting like terms on each side (so all the terms involving x on one side, and all the other terms on the other side).

1. Take 3x from both sides:
   7x + a - 3x = 3x + b - 3x
   4x + a = b
   
2. Take a from both sides:
   4x + a - a = b - a
   4x = b - a
   
3. Divide both sides by 4 (as x must be alone):
   (4x)/4 = (b - a)/4
   x = (b - a)/4 This is our answer