X^-9*x^-2
a 1/x^18
b 1/x^11
c x^18
d x^11

Exponent rule : a^-x = 1/a^x

x^-9 * x^-2 = 
1/x^9 * 1/x^2 = (when multiplying exponents with same base, add exponents)
1/x^(9 + 2) =
1/x^11

2160ft^3 i think you could use a formala to you out with this in the future

B. because the 7 represents "seven times", x represents "a number", 12 represents "plus twelve", and -4 represents "minus four"