Hello,

The general formula I have created for this problem looks like this:

Where 'n' is the age of the baby.

You can check it working:

•  the baby has just born, it gets $2000, but no deposit

2000*1.07^0-0=2000*1=2000

•  the baby turns one, it has $2000+interest + a new top up of $2000

(2000*1.07^1-0)+(2000*1.07^1-1)=2000*1.07+2000=$4140

etc. 

Note that the baby will not get a $2000 addition when he/she turns 18, but will get the interest for the previous years, so we calculate the sum for n=17, and multiply the result by the interest of 1.07 :

So the answer is $72758

Next, I check it with the online annuity calculator: