Insulin affects the glucose, or blood sugar, level of some diabetics according to the function

                                               G(x) = -0.2x² + 450,

where G(x) is the blood sugar level 1 hour after x units of insulin are injected. (This mathematical model is only approximate, and it is valid only for values of x less than about 40.) Find the blood sugar level after the following numbers of units of insulin are injected.
(a) 0 

(b) 25
Find and interpret the rate of change of blood sugar level after injection of the following numbers of units of insulin.
(c) 10 

(d) 25