X– 14 = 13 does this equal 27 or -27

!! 10 ! a westbound jet leaves central airport traveling 635 miles per hour. at the same time, an eastbound plane departs at 325 miles per hour. in how many hours will the planes be 1900 miles apart?

Joe has a rectangular chicken coop. the length of the coop is 4 feet less than twice the width. the area of the chicken coop is 510 square feet. what is the length of the chicken coup?

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.