You actually aren't supposed use to the Pythagorean Theorem. You are supposed to implement the trigonometry functions.
The angle, 60, is directly opposite with what you're trying to find, y. Also since you have another side of the triangle that is identified, you can figure what trig function to use. The line next to the angle is the adjacent. We have the adjacent and opposite. The trig function that implements both sides is the Tangent. The formula for it is tangent(angle) = opposite/adjacent.
Now substitute the number into the formula.
tan(60) = y / 5
We need to isolate y, so we times 5 and tan(60)
tan(60) x 5 = 8.66
y is now isolated and the answer is 8.66 = y
