Part (a)
r = radius
h = height = 5r
SA = Surface area of a cylinder
SA = 2pi*r^2 + 2pi*r*h
SA = 2pi*r^2 + 2pi*r*5r
SA = 2pi*r^2 + 10pi*r^2
SA = (2pi+10pi)*r^2
SA = 12pi*r^2
Answer: 12pi*r^2
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Part (b)
r = radius
h = height = 5r
V = volume of a cylinder
V = pi*r^2*h
V = pi*r^2*5r
V = 5pi*r^3
Set this equal to the stated volume of 1715pi cubic cm and solve for r.
The pi terms cancel
So,
V = 5pi*r^3
1715pi = 5pi*r^3
1715 = 5r^3
r^3 = 1715/5
r^3 = 343
r = CubeRoot(343)
r = 343^(1/3)
r = 7
Answer: The radius is 7 cm