Please help with distance and rate problem

Juan starts off on his bicycle at 8 mph. one-half hour later, Juanita starts riding along the same route at 12 mph. How long will it take Juanita to catch up with Juan?

Please explain the steps so I can learn, thank you!

Juan's speed = 8mph

In 1/2 hour, Juan has already rode 4 miles. Assume t is the time it'll take Juanita to catch up to Juan.

12t = 4 + 8t

4t = 4

so it'll take 1 hour for Juanita to catch up with Juan.