Answer :

20-3.67=16.33
then u do 16.33 divided by .37 and would get 44.1351351535....
so the most u can get is 44 stamps
Given:
Total amount = $20
Spent amount = $3.67
Price of a stamp = $.37
Now,
Total money left = $20 - $3.67
                         = $16.33
Now,
Total stamps that can be purchased = total money left / price of a stamp
                                                      = $16.33 / $.37
                                                      = 44.13513514
                                                      = 44
                                               
So, he could purchase 44 stamps