m2 differentiation

Alfred is suffering from high blood pressure and his doctor suggests he need some medication. After taking a first pill for t (0 ≤ t ≤ 15) hours, his systolic blood pressure
18 ( t + 6)^2
P mmHg is given by P= ------------------
3 t + 4

(a) Find Alfred's systolic blood pressure when he just takes the first pill.

(b) How long does it take for his systolic blood pressure to attain the minimum after
taking the first pill ? Find the minimum systolic blood pressure.

(c) It is desirable to maintain Alfred's systolic blood pressure not higher than
126 mmHg. When should he take the second pill?

i want to ask why not 18(t+6)^2 / 3t+4 ≤ 126 ???

the answer key said that 18(t+6)^2 / 3t+4 = 126