Please help me!!! please i need CHECK!!! ONLY THANK YOU?

Gwen purchased 28 items, spending a total of $108. Balloons coast $3 each, bags of candy cost $4 each, and caps cost $5 each. As students walked by, she gave each student one of each. however, after 7 students, she found that she had run out of ONE OF THE ITEMS. how many of each did Gwen purchase?