7. Given the function $f(x)$ satisfies $f(m+n)=f(m) f(n), f(1)=3$, then $\frac{f^{2}(1)+f(2)}{f(1)}+\frac{f^{2}(2)+f(4)}{f(3)}+\frac{f^{2}(3)+f(6)}{f(5)}+\frac{f^{2}(4)+f(8)}{f(7)}=$ $\qquad$
$$
\text { Original expression }=2\left[\frac{f(2)}{f(1)}+\frac{f(4)}{f(3)}+\frac{f(6)}{f(5)}+\frac{f(8)}{f(7)}\right]=8 f(1)=24 \text {. }
$$