Let the unknown number be y. We can list the equation out by the clues given. 5y + 12 = 52 Then solve this as simple algebra! Shift +12 to the other side and be - 12 5y = 52-12 5y = 40 Shift x5 to the other side and be ÷5 y = 40 / 5 y = 8 Therfore the unknown number is 8.