Answer
12 and 16 mph.
Work Step by Step
Since the faster one, f, travels 4 miles an hour faster than the slower person, for whom we will give the variable s, we know:
$ f = s+4$
We also know from the definition of speed (distance over time) that:
$ 112/4 = f+s$
We substitute to find:
$ 112/4 = (s+4)+s$
Now, we use PEMDAS, a method for simplification. This acronym reminds us that we must first address parentheses, and then exponents. Next, we address multiplication and division, going from left to right. Lastly, we simplify addition and subtraction from left to right. This gives:
$ s= 12 mph$
We substitute back into the other equation to find:
$f = 16 mph$