For a right triangle, we have he advantage of using the trigonometric functions like cosine and sine.
If you use cosine function:
cos45 = adjacent/hypotenuse
cos 45 = b/c
c = b/cos 45
If you use sine function:
sin 45 = opposite/hypotenuse
sin 45 = a/c
c = a/sin45
From the choices, the answer is b over cos 45 degrees
