The formula for your situation is this:
[tex] n^{2} =PN(PN+MN)[/tex]
where your PQ is [tex] n^{2} [/tex]
So our formula, filled in and solving for PQ is this:
[tex] n^{2}=11.5(11.5+24) [/tex]
and [tex] n^{2} =11.5(35.5)[/tex]
and n = 20.2 or 20 rounded. That's the last choice above
