Answer:
72÷6=12
so at the nursery it cost $12 per shrub
66÷6=11
so at the store it cost $11 per shrub
so if you buy 21 shrubs from the nursery it will cost: 12×21=$252
but if you buy 21 shrubs from the store it only cost: 11×21=$231
$252-$231=$21
The slope of this line is m=0
Volume= Length • Width • Height
Given info: 6•8•9= 432cm cubed