I don't get my Math

Question

An air traffic controller is tracking two planes. To start, Plane A was at an altitude of 1200

 meters, and Plane B was at an altitude of 816

 meters. Plane A is gaining altitude at 10

 meters per second, and Plane B is gaining altitude at 18

 meters per second.

Let 

x

 be the number of seconds that have passed.

(a)	For each plane, write an expression for the altitude of the plane after x	seconds.
AltitudeofPlaneA(in=meters)
AltitudeofPlaneB(in=meters)
(b)	Write an equation to show when the two planes would be at the same altitude.

Answer 1

Plane A: h(x) = 1200+10x

Plane B: h(x) = 816+18x

set them equal to find x that makes height equal

1200+10x = 816 +18x

18x-10x = 1200-816

8x = 384

x = 384/8 = 48 seconds for both planes to be at the same altitude

that altitude = 1200+10(48) = 1200+480= 1680 meters for Plane A

= 816+18(48) = 816+864 = 1680 meters for Plane B