C) 6√2
1) Examining this triangle, we can conclude this is a right triangle and state that we can find the missing side (the adjacent leg) to angle 45º using the following trigonometric ratio Cosine:
2) So we can plug into that the given values for those legs:
Note that we cross multiplied those ratios, and divided them by 12. Finally, to get rid of the fraction x/6 we multiplied that by 6 on both sides.
3) Hence, the answer is 6√2