Answer:
21 is a composite number
Step-by-step explanation:
It is a composite because multiple numbers can go in it like 3 and 7 so it is a composite number
Ummm explain the question more but b seems to make the most sense
we have been asked to find the sum of the series

As we know that a geometric series has a constant ratio "r" and it is defined as

The first term of the series is 
Geometric series sum formula is

Plugin the values we get

On simplification we get

Hence the sum of the given series is
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Answer:
B. 54π
Step-by-step explanation:
Surface area of cylinder = 2πrh + 2πr²
Radius = 3 cm
Height = 6 cm
Plug in the values
Surface area of the cylinder = 2*π*3*6 + 2*π*3²
Surface area = 36π + 18π
Surface area = 54π