To find the length of the skateboard ramp, we need to look at the triangle where the length of the skateboard ramp is a hypotenuse, a horizontal distance is a leg and a vertical distance is a leg also. So we can use Pythagorean theorem.
c² = a² + b²
c² = 17² + 4² = 305
c=√305≈17.46
Answer is 17.46 feet.