Don put $3,000 in a savings account with an interest rate of 5% for three years. if the interest is compounded annually, how much money will he have at the end of the three years?

Compounded anually means
if you put x in at y percent then 
you calculate like this
if you put in x at y percent then  the money you earn is
x +(x times y)=z=first year
second year=z+(z times y)=s
third year=s+(s times y)=t

percent means parts out of 100 so 5%=5/100=0.05
'of' can be translated as multiply
so

3000 +(3000 times 0.05)=3150=fisrt year
3150+(3150 times 0.05)=3307.5=second year
3307.5 +(3307.5 times 0.05)=3472.88=tird year

he will have 3472.88  at end of 3 years