We can find the value of an expression when given the values of \(x\), \(y\), etc. To find the value of an expression, we need to substitute the given values for \(x\) and \(y\) into \(3x + 5y\).

The plural of formula is formulae or formulas. Formulae contain equals signs, as do equations, so it can sometimes be difficult to tell the difference between an equation and a formula.

A maths question has left people in tears as it seems impossible to solve, but there's a very simple trick to working out the answer - can you solve it?