The formula for compound interest is:

Given data:

a. After ten years, that is t = 10 years, the amount in the account will be

b. After twenty years, that is t = 20 years, the amount in the account will be:

c. The time it takes for Harry's initial account value to double will be:

Therefore, the time it takes Harry's initial account to double is approximately 11 years
S=d/t
for liam
4=.25/t
t=.25/4
t=0.0625hours
for harper
t=0.25/4.5=0.055hours
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