Which number in the monomial 215 x to the 18th power y cubed z to the 21th power needs to be changed to make it a perfect cube?

For a monomial to be a perfect cube, each variable’s exponent must be divisible by 3, and the coefficient must also be a perfect cube. The exponents 18, 3, and 21 are all divisible by 3, but 215 is not a perfect cube. So the number that needs to be changed is 215, choice B.

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