Let the amount be a and rate of interest be r compound interest = $$a(1+r)^{2}-a$$ $$a(r^{2}+2r)$$ = 7716.72. $$(r^{2}+2r)$$ = 7716.72/15,800
solving the abobe quadratic equation,we get r =0.22 Hence rate of interest is 0.22