The best way to answer such questions is to first know what you are asked to find then write out what u are given then look for all possible ways to solve it
When you look at your choices, we see that 8 is not a factor of 36 and 9 is not a factor of 48. the last choice of 6 is not larger than 6, ...so 12 is the only appropriate answer as it is a factor of 36, 48, and larger than 6.
