Question

Thus was really hard and took me a long time to process

Answer 1

Since each three prices are multiples of 4, you want to list the multiples of 4.
4,8,12,16,20,24......
now, choose three of those multiples that add up to 24. for example- 4,8,12 (4+8+12=24). another example would be 16 and 8.

Answer 2

12 I think because its half 24 and 3 x4 =12