(a)
The height of PQRS is k units, since it is bounded above by the line y = k.
The length would be |OS| + |OR|, which is exactly the same length as |OQ| + |OP|. At Q, y = k (since it lies on the line y = k), sub this into the formula of the curve and hence x = -sqrt(12 - k) (since q is on...