14. (3 points) $A$ and $B$ bought the same number of sheets of letter paper. $A$ put 1 sheet of paper in each envelope, and after using all the envelopes, 40 sheets of paper were left; $B$ put 3 sheets of paper in each envelope, and after using all the sheets of paper, 40 envelopes were left. They both bought $\qquad$ sheets of letter paper.
【Solution】Solve: $(40 \times 3+40) \div(3-1)$,
$$
\begin{array}{l}
=160 \div 2, \\
=80 \text { (pieces); } \\
1 \times 80+40=120 \text { (sheets); }
\end{array}
$$

Answer: They all bought 120 sheets of stationery.
Therefore, the answer is: 120.