Originally Posted by
jgedwa
Equations can be solved in different ways.
Might I suggest solving for r. Which gives you r = (P - n)/e. But the real insight is think real, real hard about the one way to get the value of r in that equation to be 0. I think there is just one way. Once that is solved, then the remaining variables in the equation are easy to fill in.
jim
I would prefer not to think about how to get r to zero.