If he's going back using the same roads, then he would have to drive 4km west and then 3km north. If he wants to go diagonally straight to the point of his beginning, then you apply the Pythagorean theorem. c2 = a2 + b2 - the 2 means squared
c2 = 4squared + 3squared
c2 = 16 + 9
c2 = 25
c = SquareRoot of 25
C = 5
If he goes diagonally, then he needs to travel 5km.
