600 elves
25% = 1/4
1/4 of the total = 150.
1/4 x 4 = 1 (total)
150 x 4 = 600
there are 600 elves

just to clarify the engineering notation, E6 is just 1 and 6 zeros, or a million, thus, 107,000,000 is just 107E6.
We can use the equation 45m < 481
we can replace m to see where it caps.
and the cap is 10.
we can replace m to check our work
45(10) < 481
450 < 481
if you add another student, it would go over the limit.
hope this helps :D