A band playing music at a frequency `f` is moving towards a wall at a speed `v_(b)`. A motorist is following the band with a speed `v_(m)`. If `v` is the speed of sound, obtain an expression for the beat frequency heard by the motorist.

Explanation

To solve the problem of finding the beat frequency heard by the motorist following a band moving towards a wall, we can break down the solution into several clear steps.

### Step 1: Understanding the Setup
We have:
- A band playing music at frequency \( f \).
- The band is moving towards a wall at speed \( v_b \).
- A motorist is following the band at speed \( v_m \).
- The speed of sound is \( v \).
...