7. (6 points) $99999 \times 77778+33333 \times 66666=$
【Solution】Solution: $99999 \times 77778+33333 \times 66666$,
$$
\begin{array}{l}
=99999 \times 77778+33333 \times(3 \times 22222), \\
=99999 \times 77778+(33333 \times 3) \times 22222, \\
=99999 \times 77778+99999 \times 22222, \\
=99999 \times(77778+22222), \\
=99999 \times 100000, \\
=9999900000 ;
\end{array}
$$

Therefore, the answer is: 9999900000 .