If you invest $3,900 at a 7.83% simple annual interest rate, approximately how long will it take for you to have a total of $10,000?

apply simple interest formula

future value = present value (1+n*rate)

n=number of years

rate = annual interest rate in decimal

plug in values,

1=3900(1+0.0783*t)

1+0.0783t=1/3900

t=(1/3900-1)/0.0783

=19.98 years.

with compound interest,   future value=present value (1+rate/n)^(nt)

n=1,rate=0.0783, future value=1, present value=3900,

t=log(1/3900)/log(1.0783)=12.49 years.

i do not know the answer i am sorry