Answer:
16
Explanation:
Darren completely filled each box before the 21st box. This means he completely filled 20 boxes. To find out how many tins fit in each box, divide:
496/20 = 24.8
This means each of the 20 preceding boxes held 24 tins. To get these filled, Darren used 20(24) = 480 tins of juice.
This left Darren with 496-480 = 16 tins of juice to put in box 21 before lunch.