Let's write an equation describing the problem.
Any even whole number may be represented by writing
in which 
is any non-negative integer.
It follows that for a even whole number the next (consecutive) even whole number can be written as 
.
We now need to solve the following equation:
If we solve for we get:
We have to values, as the equation is quadratic. We take the positive one as the correct one. So
, and if we plug in this value to and we know that the asnwer is 16 and 18.
Any even whole number may be represented by writing
It follows that for a even whole number
We now need to solve the following equation:
If we solve for
We have to values, as the equation is quadratic. We take the positive one as the correct one. So