To find the biggest number of boxes needed, you need to find the highest common factor for both of 48 and 32
Finding the highest common factor:
48 = 2^4 x 3
32 = 2^5
Take the number that has a common base and lowest index from both of them:
2^4
= 16
Since 16 is the highest common factor of both of them, he will need 16 boxes at most (3 gold coins and 2 silver coins in each)