You need 3 sticks of butter for every 24cookies you bake

So (2 times 10^21)/(8 times 10^3)
using the associative property
exg
xy/zt=y/z times x/t so

(2 times 10^21)/(8 times 10^3)=2/8 times (10^21)/(10^3)
2/8=1/4=0.25

when dividing exponents, just subtract the bottom number from the top number exg
10^21/10^3=10^(21-3)=10^18

so the answer is 0.25 times 10^18, but

scientific notation is
(a number >1 and <10) times 10^x

so 0.25 times 10=2.5 and 2.5>1 and <10 so this should work

0.25 times 10^18=2.5  times 10^17 ( we just took the ten from the 18)

so the answer is 2.5 times 10^17 or C