Answer:
7.8
Explanation:
First I will try 50. I got 127,550, so that was way too big.
Let me try a smaller number. How about 5. I got 155, so that was a bit too small.
Now I'll try 20. I got 8420. Looks like the number is between 5 and 20.
How about 7. I got 399.
Let me try 8. I got 584! That's really close. It's just a little too big.
I tried 7.5, and got 485.624. So close! Just a little higher.
Putting in 7.8 yields 543.192! That's our answer.