A straightforward way to solve is to consider the slope of the line, 1/2, which means that for a rise of 1, we have a run of 2.
The hypotenuse length was obtained using the Pythagorean theorem. Then notice that . That means that for a run of 4 (or -4) and rise of 2 (or -2) starting from B we get to C.
So C = (5, 3) or C = (-3, -1).