$$33+18\times4=105$$  $$105\div7=15$$ 
The fruit store sold a total of $$33$$ boxes of apples in the first three days of last week, and an average of $$18$$ boxes of apples per day in the last four days. How many boxes of apples did this fruit store sell on average each day last week? 
Options:
[1] $$13$$ 
[2] $$14$$ 
[3] $$15$$ 
[4] $$16$$ 