Changing the subject of a formula

A very good day everyone. I am urgently requesting for your help for this taxing mathematics questions, all relating to algebra (changing the subject of a formula).

If you could help me to explain those sums I would be very gratified. So here they are:

**In each of the following cases, rewrite the equation such that the letter in the square brackets is the subject of a given formula.**

1. $\displaystyle 1/u + 1/v =1/f$ **[u]**

2. $\displaystyle y = 3x + 5/2-z$ ** [z]**

3. $\displaystyle T = 2\pi \sqrt{L/g}$ **[g]**

4. $\displaystyle s = v^2 - u^2 / 2a $ **[u]**

5. $\displaystyle y = t^2 - x^2 / t^2 + x^2$ **[x]**