Use the two conditions to solve for C and k

Is time measured in hours or minutes?

5000 = C e^(k15)

40000 = C e^(k60)

Divide the second by the first, side by side:

8 = e^(60k-15k)

8 = e^(45k)

ln 8 = 45k

k =ln8 /45

Plug into one of the conditions above to find C. C is the original population, because it is the y-value at t=0.

Good luck!!