4. duane and roberto joined a rock-a-thon
to raise money for the local animal
shelter. duane rocked for 10-hours and
roberto rocked for 13-hours. how much
longer did roberto rock than duane?

Roberto rocked 3 hours longer than Duane.

roberto rocked for 3 more hours

Step-by-step explanation:

13-10=3

256π units²   (answer b)

step-by-step explanation:

the formula for the surface area of a sphere of radius r

is             a = 4πr²

and so, if r = 8 units, then the surface area is:

a = 4π(8 units)² = 256π units²   (answer b)