I think you wrote that incorrectly
Answer:
A. 
Step-by-step explanation:
The formula for the volume of a cylinder is the formula for the area of the circle, times the height of the cylinder. The formula for the volume of a circle is,

Multiply that by the height to find the formula for the volume of a cylinder,

Where (pi) represents the value (3.1415), (r) represents the radius, and (h) represents the height of the cylinder. Now substitute in the given values, remember, this problem gives the diameter of the cylinder, divide that value by two to find the radius.

I think you want the least common multipule (exg LCM of 2,3,4 is 12)
so we find the factors and include all of them so like this
15=3 times 5
12=2 times 2 times 3
8=2 times 2 times 2
so to include all of them we include 3 2's, 1 3 and 1 5 or 2 times 2 times 2 times 3 times 5 or 8 times 15 or 4 times 30 or 120
the LCM is 120
so 4/15=32/120
1/12=10/120
3/8=45/120
add 32/120+10/120+45/120=(32+10+45)/120=87/120
15
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