Because the triangle is a right angle, the hypotenuse is the square root of the sum of the legs squared or the square root of (20 ^2 + 15^2) or 25. The distance wayne computed was the distance from Ferris to Dunlap or 15 plus the distance from Dunlap to Butte or 20 or 35 miles all together. The difference of 35 and 25 is 10