Since this is a right triangle, we can use our trigonometric functions to solve for x.
Since we know the adjacent side and hypotenuse, we will use cosine.
Based on the function

, we can solve for x. The adjacent side is 7 and the hypotenuse is 12. Plugging this in, we get

.
Now, we must use our inverse trigonometric functions to solve for x:

The inverse cosine and cosine on the left side cancel, leaving you with:
