Prove that the sum of four consecutive whole numbers will always be even.

First, check you understand what the question's asking by determining the key words. Next, try a couple of examples to convince yourself that the statement does in fact work, i.e 1+2+3+4=10, which is even.
Now, rather than specific examples let's take the number 'x'. The next consecutive whole number after x will be x+1, after that will be x+2 and so on. We can now call our four consecutive numbers x, x+1, x+2, x+3.
So, when we 'sum' these 4 numbers we get;
x + (x+1) + (x+2) + (x+3) = (x+x+x+x) + (1+2+3) = 4x + 6.
If we look carefully at '4x + 6', we should be able to factorise this quite easily. If we rewrite it as the following;
4x+6 = 2(2x+3).
We can see here that the answer is even, as it will always be a multiple of 2, no matter what value we take 'x' to be.