SOH CAH TOA
In this case we have hypotenuse 18 and adjacent angle 45
h & a would be cosine so:
cosine 45 = a/18 ( you are gonna need a calculator if u happen to find this a question like this again)
0.52532198881 = a/18 then we use algebra
0.52532198881 * 18 = 9.45579579858
Your answer is A., rounding the number above.