I=PRT
x=(100)*(0.03)*(2)
x=6
100+6=106
To find the amount of money you'll have saved after 2 years of not touching it, you have to find the interest first. To find the interest, you multiply the principle (100) by the annual interest rate (3%/0.03) and the rate by time in years (18-16=2)
100*0.03*2=6
Now, you add the interest (6) to the original investment (100) you get 106.
If you don't touch your inputted initial amount until you're 18, you will have 106 dollars.