Ok so I don't really know how to explain this well except that you have to mess around with the numbers to see what divides to 43. I tried things like 103÷7, and 107÷3. It's a little bit easier since you can't divide by zero (so don't try something like 731÷0) and if you divide by one, you'll just get the same answer (like 307÷1=307) . This eliminates a lot of your number combinations.
I found out that 301÷7 gives you the magic number of ...43!!! I hope this makes sense to you, if it doesn't, let me know :D.