The diagram shows the velocity–time graph for an athlete running in a straight line. Her velocity \(t\) seconds after passing a fixed point \(O\) is \(v\text{ m s}^{-1}\). The graph has four straight line segments. She is at \(P\) when \(t=90\).

(a) Find the distance \(OP\). [2]

(b) Find the total distance run in the 90 s after passing O. [1]