Fundamental Theorem of Calculus

Solon Container receives 450 drums of plastic pellets every 30 days. The inventory function (drums on hand as a function of days) is I9x)= $\displaystyle 450-\frac{x^2}{2}$

A. Find the average daily inventory (that is, the average value of I(x) for the 30-day period)

B. If the holding cost for one drum is $0.02 per day, fidn teh average daily holding cost (that is, the per-drum holding cost times the average daily inventory.)

I have no clue how to do this.

We have learned the F(b)-F(a) formula and that the derivative of the integral is the function.

Thanks!