Verified answer

3 dogs x (2 cans/1 dog) x (7 days/1 week) = 42 cans/week

Successive labels cancel out by num & denom,

Sam has to buy 42 cans per week whenever he shops.

If you think about this, since each dog eats

2 cans per day, that means with 3 dogs,

(3 x 2 = 6 cans per day). Since he only shops

once a week, in 7 days, the dogs

will have eaten 6 x 7 = 42 cans.