Question 41786
The general formula is
{{{A = P*(1 + I/100)^t}}}

where P = principal that becomes amount = A in 't' years at the rate I% compound interest per annum.

Here I = 6% per year and time t = 2 years.

Put P = 7800, I = 6 and t = 2 in the formula.
You get 
{{{A = 7800*(1+6/100)^2}}}
= {{{7800*(1.06)^2}}}
= 7800 x 1.1236
= 8764.08


Thus, $7800 becomes $8764.08 after 2 yrs. at the rate 6% compound interest per annum.