Just substitute a pair of (p, s) into the equations in the options and see which one is always true.
For example, take the pair (p, s) = (13, 1) and the option \(p = \dfrac s9 + 4\). When we substitute it into the equation, it is not right, since 13 is not 1/9 + 4. So this option is not the correct answer. Repeat this until you find the one that will give you a correct equation.