Answer
$36$ plants
Work Step by Step
Step 1. Assume the thief stole $x$ number of plants originally. After meeting the first guard, he had $x-\frac{x}{2}-2=\frac{x}{2}-2$ plants left.
Step 2. After meeting the second guard, he would have $\frac{x}{2}-2-\frac{x/2-2}{2}-2=\frac{x}{4}-3$ plants left.
Step 3. After meeting the third guard, he would have $\frac{x}{4}-3-\frac{x/4-3}{2}-2=\frac{x}{8}-\frac{7}{2}$ plants left.
Step 4. Since $\frac{x}{8}-\frac{7}{2}=1$, we have $x=8+28=36$ plants.
