A concave mirror gives a real image magnifies 4 times. When the object is moved 3 cm the magnification of the real image is 3 times. Find the focal length of mirror.

Explanation

To solve the problem step by step, we will use the mirror formula and the magnification formula for a concave mirror.

### Step 1: Understand the given information
- A concave mirror produces a real image that is magnified 4 times (M1 = -4).
- When the object is moved 3 cm, the magnification becomes 3 times (M2 = -3).

### Step 2: Set up the magnification equations
The magnification (M) for mirrors is given by the formula:
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