You are looking for the least common multiple, or the smallest number that is divisible by both given quantities. For this problem, we can accomplish this by listing out the multiples of each number
[tex]4 \: 8 \: 12 \: 16... \\ 6 \: 12 \: 18...[/tex]
here we can see that 12 is the smallest common multiple, and is the smallest number of baskets Jessica can put together without waste.