Answer:
They should use 9 large buses
Step-by-step explanation:
First; determine the cost per person for each bus.
$500 / 30 seats = $16.66 per student
$750 / 50 seats = $15.00 per student
Therefore it is cheaper for the school to use the large buses exclusively.
They can book 9 large buses at the cost of ($750 * 9) = $6,750 and not use all the available drivers.
Another alternative that some might use would be:
30x + 50x = 450
80x = 450
x=5.625
30(5) + 50(6)
150+300 = 450
($500 * 5) + ($750*6) =
$2500 + 4500 = $7,000
The price though is more that just booking 9 buses and thus not the correct answer.