Percent of the original amount of the smoke per minute t

Question

Question: AIR PURIFICATION To test air purifiers, engineers ran a purifier in a smoke-filled 10-ft × 20-ft room. While conducting a test for a certain brand of air purifier, it was determined that the amount of smoke in the room was decreasing at the rate of

R(t) = 0.00032t⁴ - 0.01872t³ + 0.3948t² - 3.83t + 17.63   (0 ≤ t ≤ 20)

Percent of the (original) amount of the smoke per minute, t min after the start of the test. How much smoke was left in the room 5 min after the start of the test? Ten min after the start of the test ?