Answer :
The future value for simple interest is given by the following formula:
[tex]A=P(1+rt)[/tex]Where A is the future value, r is the rate of interest, t the time and P the present value. Now we solve for the rate of interest "r" first by dividing both sides by "P":
[tex]\frac{A}{P}=1+rt[/tex]Now we subtract 1 to both sides:
[tex]\frac{A}{P}-1=rt[/tex]Dividing both sides by "t":
[tex]\frac{A}{Pt}-\frac{1}{t}=r[/tex]Replacing the known values:
[tex]\frac{11349}{(7800)(7)}+\frac{1}{7}=r[/tex]Solving the operations:
[tex]0.35=r[/tex]Therefore, the annual rate of interest is 35%.