(In reply to
Solution by Jer)
I was helping some students prepare for a math counts competition this afternoon by doing an old sprint round test. This problem was on it, albeit with three of the variables given, solve for the fourth.
I had no memory of this one  yet I was the only one to post about it less than a year ago!
After solving it easily enough I made a note work on a generalization when I got home. I did so, analytically this time and the result was nice so I thought I'd post it here  if it wasn't here already. So I did a search and lo and behold...

Posted by Jer
on 20180105 22:07:04 