How long can you afford to stop for lunch if you can drive a steady 90 km/h on the highway and must take a 225 km trip in 210 min?

1 hour

Explanation:

The trip is 225 km long, and your speed is 90 km/h.  The time it takes to complete the trip without stopping is:

t = (225 km) / (90 km/h)

t = 2.5 hours

t = 150 minutes

You must complete the trip is 210 minutes, so you can afford to stop for 60 minutes, or 1 hour.