In a sealed vessel of fixed volume, the pressure P (in kPa) of a gas is P=8.31T, where the temperature T (in K) varies with time t (in minutes) according to T=300+4t−0.1t2 for 0≤t≤40. At what time is the pressure increasing at 20 kPa per minute?
a) 12 min
b) 8 min
c) 20 min
d) 16 min