(a)

Place the two prisms beside each other. Confirm that their bases are placed opposite side of the incident white light and faced to each other. When white light is incident on first prism, it gets dispersed. Subsequently this dispersed light is incident on second prism. As a result we this light recombined and emerge from the combination of two prisms.

(b)

Let consider the above conditions, if we can increase the angle of glass prism, it leads to deviations of the light because of the combination of the prism become euqal. As a results, light from the pencil will disperse without much deviation.