When do you use algebra in the real world?

Algebra may seem really stupid in school, but it does serve a purpose through life. For example if you had $x and you can get 40 litres of petrol, 1 litre costing $1.20? Here's how you do it using algebra. 1=$1.20 40=$1.20x40=$48 .'.x=$48 Hope this helps, but I suck at maths.