To find how many rows you will make if you run the oven for 12 ¼ hours and can produce 640 rows per hour, we multiply the number of rows per hour by the number of hours.

Step-by-step calculation:

1. Convert 12 ¼ hours to a decimal: $12 \frac{1}{4} = 12 + \frac{1}{4} = 12 + 0.25 = 12.25 \text{ hours}$

2. Multiply the number of rows per hour (640) by the total hours (12.25): $640 \times 12.25 = 7840 \text{ rows}$

So, you will make 7,840 rows.

Would you like more details or further explanation?

Here are 5 related questions you might consider:

1. How do you convert fractions into decimals for time calculations?
2. What if the oven runs for a different amount of time, say 10 ½ hours?
3. How would the answer change if the rate of production increased to 700 rows per hour?
4. What would happen if the oven efficiency dropped and you could only make 500 rows per hour?
5. Can we use this method to calculate for multiple ovens running simultaneously?

Tip: When working with fractions of hours, always convert to decimal form to simplify calculations.