Answer :

There are multiple answers:
• if he has 36 vases, he would be able to put one tulip in each. 
• if he has 18 vases, he would be able to put two tulips in each
• if he has 12 vases, he would be able to put three tulips in each 
• if he has 9 vases, he would be able to put four tulips in each
• if he has 6 vases, he would be able to put six tulips in each 
• if he has 4 vases, he would be able to put nine tulips in each 
• if he has 3 vases, he would be able to put twelve tulips in each
• if he has 2 vases, he would be able to put eighteen tulips in each 

Essentially you are looking to find out what the multiples are and then dividing to find the number of tulips.