Hi
Let x and (1500-x) represent the number of non-students and students respectively
Question states*** 50% of $12 = $6 (half price)
$12x + $6(1500-x) = $15600
$6x = $15600 - $9000
$6x = $6600
x = 1100, number of non-students. Students numbered 400.
CHECKING our Answer
$12*1100 + $6* 400 = $13200 + $2400 = $15600