Richard P. answered 04/04/20
PhD in Physics with 10+ years tutoring experience in STEM subjects
To start, set up the differential equation. It is:
d P(t) / dt = 6 t1/2
This type of differential equation can be solved by the method of separation of variables.
d P = 6 t1/2 dt
Integrating both sides gives P = 4 t3/2 + C where C is a constant of integration.
Since we know P(0) = 600 we see that C = 600, so the particular solution we need is thus
P(t) = 600 + 4 t3/2
Plugging in t = 7 gives P(7) = 674.