Same here, we do a quick switcharoo on the variables first,
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Here are some simple equations that can be a life saver with this stuff :
vol of a sphere =

Circumference =

sorry this might not be very helpful. I haven't don't this since last year. You basically have to work backwards. so plug in 972 for V and then do (3/4)×3.14.
then take the answer u got for ^^ and divide it by 2? not sure.
Make the equations equal to each other to find x.
21.2x+c=5.3(4x-4.6)
Now distribute.
21.2x+c=21.2x-24.38
So c= -24.38
(a,7) lies on the equation of 5x-y=8, that means we solve for x when y=7.
5x-(7)=8
5x=8+7=15
x=3
=>
a=3