7. (3 points) On Tree Planting Day, a batch of saplings needs to be planted. If A plants them alone, it takes $\frac{1}{3}$ more time than B planting them alone. If A and B plant together, B plants 36 more saplings than A. How many saplings are there in total? $\qquad$ 


【Analysis】We consider the time taken by person B as 1, and the time taken by person A is $1 \times\left(1+\frac{1}{3}\right)$. We find the difference in their work efficiency, and then divide 36 by this difference to get the number of trees planted by B, and further determine the total number of trees.

【Solution】Solution: The work efficiency of B is: $1 \div 1=1$
$$
\begin{array}{l}
1 \div\left[1 \times\left(1+\frac{1}{3}\right)\right], \\
=1 \div \frac{4}{3}, \\
=\frac{3}{4} ; \\
36 \div\left(1-\frac{3}{4}\right) \times\left(1+\frac{3}{4}\right), \\
=36 \times 4 \times \frac{7}{4}, \\
=252 \text { (trees); }
\end{array}
$$

Answer: There are a total of 252 saplings.
The answer is: 252.