Solution: For X 45-seat buses, the total number of passengers can be expressed as 45x+ 15 or 60(x- 1), and the equation is as follows:

45x+ 15=60(x- 1)

45x+ 15=60x-60

60x-45x=60+ 15

15x=75

x=5

So the number of first-year students =45X5+ 15=240.