When comparing two numbers, you usually start by comparing the numbers on the left of the decimal point, if you find one of them greater than the other, then you've got your answer ready. If the numbers on the left of the point are equal, then you start comparing the decimal part.
In the two numbers given, we have 87 and 13.688. We start by comparing the numbers before the point, we will find that these numbers are 87 and 13.
Comparing these two, we can see that 87 is greater than 13.
Therefore: 87 is greater than 13.688