Explanation

 48 is the correct answer 

If one of the numbers is 72, and the greatest common divisor of the two numbers is 24, then the other number must be divisible by 24. If the least common multiple of the two numbers is 144, then the other number must be divisible by 144/72 = 2, which means that it must be even. Therefore, the other number must be an even multiple of 24. The only even multiple of 24 that is less than 72 is 48, so the other number must be 48.