MathNet 2016-part-05 — 184 problems (EN–VI) Question 129

Water pours into a tank at a constant rate. After 2 hours the tank was 36% full and after 10 hours it is 100% full. How full was the tank to begin with?
(A) 10%
(B) 12%
(C) 15%
(D) 18%
(E) 20%