If 420 miles = 20 cm on a map, how many miles is 1 cm?

How do you do this geometry problem

Find three consecutive numbers such that the sum of one-fourth the first and one-fifth the second is five less than one-seventh the third

Aprojectile is thrown upward so that its distance above the ground after t seconds is given by the function h(t) = -16t2 + 704t. after how many seconds does the projectile take to reach its maximum height?