3 is being multiplied by the square root of 18 which is being raised to the "x" value
A: company A: 12+6n, company B: 15+5n n=number of windows
B: Company A: 12+6(8)=$60, Company B: 15+5(8)=$55
company B charges less
C: Company A: 12+6(6)=$48, Company B: 15+5(6)=$45
$48-$45=$3 less to use Company B instead of Company A