$\"\"$

Speed = $\"\"$

Speed = $\"\"$ (Substitute distance = 3 miles and time = 6 seconds) $\"\"$

1 hour = 60 minutes

1 minute = 60 Seconds

So, 1 hour = 60 × 60 Seconds

1 hour = 3600 seconds $\"\"$

Speed = $\"\"$

Speed = $\"\"$ × $\"\"$

Speed = $\"\"$ × $\"\"$ (Cancel the common unit seconds)

Speed = $\"\"$ $\"\"$

Simplify, Speed = $\"\"$

Speed = 1800 miles per hour

$\"\"$

The speed is 1800 miles per hour.