Word problem

[lmf0610]

Kathleen and Cade leave simultaneously from the same point hiking in opposite directions, Kathleen walking 4mph and Cade at 5 mph. How long can they talk on their walkie-talkies have a 20-mile radius?

 

[galactus]

Tney won't be out of range until the sum of their distances is 20 miles or more.

distance =rate*time.

5t+4t=20, solve for t