Tom plants a tree that is 1 year old and 5 feet tall.  It gains 3 feet per year.  How old is it when it is 23 feet tall?
It has grown 23-5=<<23-5=18>>18 feet
So it is 18/3=<<18/3=6>>6 years older
That means it is 6+1=<<6+1=7>>7 years old
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