Find the ratio of cans of fruit to the total number of food items collected.

First add all the items together:

6 + 4 + 7 + 4 = 21

then we compare 6 and 21 and look for common factors, 6 and 21 have the common factor 3 so we divide them both by 3 to get 2 and 7. since 2 and 7 have no common factors our answer is

2:7

This means for every 2 cans of fruit there are 7 total items and vice versa.