If this is just finding what N is equal to, you can subtract 51 from 106 to get 55, and if you want to make sure it's correct, you can add 51 and 55 together to get 106
You would use estimation by rounding all the non-variable numbers to the nearest ten. For example, 51 to 50 and 106 to 110. The new equation is 50 + N = 110 and you can estimate N to be 60.
