To determine how many rosemary plants were planted, we need to recognize that the neighbors planted four different types of herbs: basil, thyme, rosemary, and oregano. Since they planted the same number of each herb and a total of 52 plants, we can set up the equation:
Let \( x \) be the number of each type of herb planted. Since there are 4 types of herbs, we have:
\[ 4x = 52 \]
Now, we can solve for \( x \):
\[ x = \frac{52}{4} = 13 \]
This means that 13 plants of each type of herb were planted. Therefore, the number of rosemary plants planted is 13.
The correct answer is:
13 rosemary plants