First, we will need to find out how much each of the bakeries accrued within 7 days. We should be able to do this by simply multiplying the amount of cakes the bakery sells each day by the amount of days it's been accruing it for.
For example:
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Since the answer doesn't explain if you're giving EACH of the bakeries amounts or combining them, that's up to you to decide if you want to do that or not.