An investment of $$16,000$ is growing at $4\%$ compounded quarterly.

a$.$ Calculate the future value of this investment at the end of year $1.$

Round to the nearest cent

b$.$ If the interest rate changed to $6\%$ compounded monthly at the end of year $1,$ calculate the future value of this investment at the end of year $4.$

Round to the nearest cent

c$.$ Calculate the total amount of interest earned from this investment during the $4-$year period.

Round to the nearest cent