To convert 400 km/h to miles per hour, you can use the following step-by-step instructions:

Step 1: Understand the conversion factor

1 kilometer is equal to 0.621371 miles.

1 hour is equal to 60 minutes.

Step 2: Set up the conversion equation

We can set up the conversion equation as follows:

400 km/h * (0.621371 miles/1 km) = x miles/hour

Step 3: Cancel out the units

By multiplying 400 km/h by the conversion factor (0.621371 miles/1 km), the km unit cancels out, leaving us with miles per hour.

Step 4: Perform the calculation

Multiply 400 km/h by 0.621371 miles/1 km:

400 km/h * 0.621371 miles/1 km = 248.5484 miles/hour

Step 5: Round the answer

Since miles per hour is typically rounded to the nearest whole number, we can round 248.5484 to 249 miles/hour.

Therefore, 400 km/h is approximately equal to 249 miles/hour.