Changing the subject

The idea

Rearranging a formula is solving it for a letter: do the same to both sides until the letter is on its own. From $v = u + at$, $t = \frac{v - u}{a}$.

1. Undo the operations around the letter, last one first.
2. Apply each step to the whole of each side.
3. Higher tier: if the letter appears twice, collect those terms and factorise.

Watch out Dividing $v - u$ by $a$ divides both terms: $\frac{v - u}{a}$, not $v - \frac{u}{a}$.