An equation is a balance: whatever is on the left weighs the same as whatever is on the right. To find the letter, peel away everything sitting next to it by doing the OPPOSITE operation — and do it to both sides so the balance holds. Order matters in a two-step equation: undo the adding or subtracting first, and only then the multiplying or dividing. Always check by putting your answer back into the original equation; it takes seconds and catches the sign slip that costs the mark.
Worked example
Problem Solve the equation 3y + 7 = 25.
Deal with the + 7 first: take 7 off BOTH sides, giving 3y = 18.
3y means 3 × y, so undo the multiplication by dividing both sides by 3.
18 ÷ 3 = 6, so y = 6.
Watch out Do not divide 25 by 3 at the start. The 7 is not part of the 3y term, so it has to come off first.