c.
The number of students is represented with S, to show 2 times that number it is shown as 2S, a less than is word problem jargon for minus. So it is 2S-21.
My math teacher said anything to the power of zero is 1
-8(1 + 8n) - 8(6 - 4n) = -24
-8 - 64n - 48 + 32n = -24
-32n - 56 = -24
-32n = 32
n = -1
-10x + 48 = -6x+24
48 - 24 = -6x + 10x
24 = 4x
x = 24/4
x = 6
