3. (8 points) Legend has it that those who can find a four-leaf clover in a field of three-leaf clovers are lucky people. One day, Jiajia was picking three-leaf clovers in a big forest. When she picked her first four-leaf clover, she found that the total number of leaves on the clovers she had picked was 40. Therefore, she already had $\qquad$ three-leaf clovers.
【Solution】Solution: $(40-4) \div 3$
$$
\begin{array}{l}
=36 \div 3 \\
=12 \text { (plants) }
\end{array}
$$

Answer: She already has 12 clover plants. Therefore, the answer is: 12.