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).

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

Write 7.264 51 correct to 3 decimal places.

Related Maths GCSE answers

complete the square by rewriting x^2+6x-15 in the form (x+p)^2-q

Solve (5 - x)/2 = 2x – 7

Rationalise the denominator of the fraction 3/sqrt(5)

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.