We want to factor the quadratic in the numerator, so we can hopefully reduce it, by canceling out the 5k + 2. You can also use polynomial division, to solve this. Anyway, by FOIL (First-Outer-Inner-Last) we gain, that the factored quadratic is (5k + 2)*(k -3). Since the 5k + 2 in the numerator cancels out with the 5k + 2 in the denominator, k - 3 is the answer.