Let's break down the information given step by step to determine the height of the rosebush when Zev planted it.
The first year it grew 3 inches.
The second year it grew 12 inches.
Zev then cut it back 5 inches.
The third year it grew twice as much as the first year.
The rosebush is now 42 inches tall.
Let's work backward to find the initial height of the rosebush.
Step 4: The third year it grew twice as much as the first year, which means it grew 3 inches * 2 = 6 inches in the third year.
Step 3: Zev cut the rosebush back 5 inches after the second year. Therefore, after the second year, the height was 12 inches - 5 inches = 7 inches.
Step 2: The rosebush grew 12 inches in the second year, so after the first year, it was 7 inches - 12 inches = -5 inches (assuming negative height indicates the rosebush was cut back to ground level).
Step 1: The rosebush grew 3 inches in the first year, so when Zev planted it, the initial height was -5 inches - 3 inches = -8 inches (again, indicating that it was initially cut back to ground level).
Therefore, when Zev planted the rosebush, its height was initially 0 inches or ground level.