I got this question, I know how to do it but the answer is never right

A weight is hung from two hooks in a ceiling by strings

of length 54 cm and 42 cm, which are inclined at 70◦ to

each other. Find the distance between the hooks.

$\displaystyle c^2 = 54^2+42^2 -(2)(54)(42) \cos 70 $

Is this right?