Our missing number we are solving for is X.
We are told x will equal 2x (number doubled) plus -16.
x = 2x + -16 We want to move the smaller variable to the right to sit with the larger one and move the -16 to the left by subtracting it from both sides. Remember that subtracting a negative is the same as adding it. So essentially we add 16 to both sides.
16 = 2x - x Combine the variables
16 = x or x = 16
I chose to put the variable on the left in this problem to avoid having a -x on the left side. It doesn't matter which side the variable is on to solve, but when you state it - we usually say x = 16.