Given m and n are positive integers such that for some positive integer, x, [math]\sqrt {x+43} =m[/math] and [math]\sqrt {x+16} =n[/math], what is the value of the product mn as a positive integer? Given m and n are positive integers such that for some positive integer x, [math]\sqrt{x+43}=m[/math] and [math]\sqrt{x+16}=n[/math], what is the value of the product mn as a positive integer?