Answer:
(a)

(b)

(c)

Step-by-step explanation:
(a)
Simply evaluate (a+h) in the function:

(b)
Evaluate (a) in the function:

Using the previous answers lets calculate f(a+h)-f(a)

(c) To find the rate of change of f(a+1) when a=7 we need to calculate its derivate at that point:

10*4230 that should do the trick for ya just multiply it and ya got answer
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C=d x pi
d= 24
C= 24 x 3.14
C=75.36 inches
hope this helps