Subtract, Then Divide

In $3x+5 = 20$, the unknown is multiplied by 3 and then 5 is added. Undo the operations in reverse order. Subtract 5 from both sides, then divide both sides by 3:

$$3x = 15$$

$$x = 5$$

Check: $3\cdot 5+5 = 20$, which is true.

In a two-step equation, each number is undone by a different operation. You subtract the 5, because it was added. You divide by the 3, because it is the coefficient. The 20 only changes through the arithmetic on the right side. If the order is unclear, say the equation in words: three times a number, plus five, is twenty.