calc extra credit wokr, i need it!!!

i'm having trouble with this last problem:

The rate of growth dP/dt of a population of bacteria is proportional to the square root of t, where P is the population size and t is the time in days. (0<=t<=10).

That is:

dP/dt = ksqrt(t) sqrt(t) = square root of t, dunno how to type that out with the keyboard.

The initial size of the population is 500. After 1 day the population has grown to 600. Estimate the population after 7 days.

any help would be greatly appreciated!!!!!