Ax By Cz=2800

x y z=12

x, y, z must be positive integers

150x 300y 500z=2800

150x 300y=2800-500

Exhaustive z

Buy one z=1 150x 300y=2300

The right side must be 3 Divisible, so there is no solution

Similarly z=3 z=4, no solution

z=5

150x 300y=300

x y z=12

No solution

z=2

150x 300y=1800

x y 2=12

At this time x=8 y=2

8 pictures 150, 2 pictures 300, 2 pictures 500