Question 862718
You want a well-worked, solved problem, but maybe you can do this if you recognize that:


The hypotenuse PLUS the vertical-pointing leg is 18 feet, and the leg on the ground is 12 feet.  You can say, y is the vertical leg, c is the hypotenuse, and therefore y+c=18.  Also, recognize that this forms a right triangle (yes, see the use of term, "hypotenuse") so you can use Pythagorean Theorem.