The diagram shows the velocity-time graph for the motion of a particle over a period of 45 seconds. The velocity of the particle at \(t=30\) is \(V\text{ m s}^{-1}\). The distance travelled by the particle in the 45 seconds is 800 m.

(a) Find the value of \(V\).

(b) Find the acceleration of the particle when \(t=35\).