Answer
$P(x)=60x-x^2$
Work Step by Step
Suppose that the positive numbers are represented by $x$ and $y$, so $x+y=60$. We want to find $P=x\cdot y$ but only in terms of $x$, so we solve the first equation for $y$:
$x+y-x=60-x$
$y=60-x$
Now, we replace that $y$ in $P=x\cdot y$:
$P=x(60-x)$
$P=60x-x^2$ And that's our answer.