Use numbers and basic arithmetic operations (+ - * /) to obtain 24. 
Input: 4 4 6 8 
Answer: (4 + 8) * (6 - 4) = 24 
Input: 2 9 10 12 
Answer: 2 * 12 * (10 - 9) = 24 
Input: 4 9 10 13 
Answer: (13 - 9) * (10 - 4) = 24 
Input: 1 4 8 8 