If you drew the map of the cities, you will make a right triangle. 51 and 60 are the two shorter sides, and the length that is missing is the hypotenuse. this is the longest side, and it's also the side you are trying to find the length of. Using the Pythagorean theorem ,a^2 + b^2 = c^2, you can find the hypotenuse.a = 51. b = 60. and c is the unknown. so you plug in the numbers where they belong, 51^2 + 60^2 = ?. 5^2+60^2=6021. The square root of 6201 is 78.74, which is rounded to 79. So A. 79 is the correct answer.
Hope I helped!:)
