Answer:
9 hours
Explanation:
Using the initial ratio of 15 tickets in half an hour, you can set up a proportion (equivalent ratios) to find the amount of time it would take to sell 270 tickets:

Where 'x' is the amount of time to seel 270 tickets.
Cross-multiply: 0.5(270) = 15x or 135 = 15x
Divide: 15x/15 = 135/15 or x = 9 hours