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756pi  unit^3.

Step-by-step explanation:

This is the sum of the volume of 3 spheres

V of a sphere = 4/3 pi r^3, so we have:

4/3 pi 2^3 + 4/3 pi 6^3 + 4/3 pi 7^3

= 4/3pi (2^3 + 6^3 + 7^3)

= 756pi.

21

step-by-step explanation:

x-3y=4

step-by-step e