What is the speed of the faster plane?

Two planes pass over Topeka at the same time, traveling in opposite directions. The rate of the faster plane is 20 mph greater than the slower plane. After 4 hours the planes are 800 miles apart. What is the speed of the faster plane?

Find two ways to solve it.



Thanks!What is the speed of the faster plane?let x = speed of faster plane

let x-20 = speed of slower plane



4(x) + 4(x-20) = 800

4x + 4x - 80 = 800

8x = 880

x = 110 mph



or...



let x = speed of slower plane

let x+20 = speed of faster plane



4(x) + 4(x+20) = 800

4x + 4x + 80 = 800

8x = 720

x = 90 mph

x+20 = 110 mph