For part (a), it says you must change the experimental setup so using a stronger magnet will increase the emf.
For part(b), It wants you to sketch the emf wrt to time. The plane of the coil in the position shown in the diagram is enclosing maximum flux, so on the flux vs time graph, it would start at a maximum turning point. We know that emf is the negative gradient of the flux vs time graph and so the graph would start from zero, reach a maximum, reach a minimum and then go back to zero.
BTW: It is max/min because these are slip rings and so it is AC.
I hope that helps (PS. sorry for the late reply i just realised the date of the post but why not answer it anyway)