word problem equations and inequalities

Question

A plane leaves an airport traveling at an average speed of 240 kilometers per hour. How long will it take a second plane traveling the same route at an average speed of 600 kilometers per hour to catch up with the first plane if it leaves 3 hours later?

Answer 1

Start the clock at x when the 600 kilometer per hour plane leaves.

The 240 kilometer per hour plane would have traveled x+3 hours by then.

So 240(x+3) = 600x

240x + 720 = 600x

360x = 720

x = 2 hours to catch up