An efficiency study conducted for Elektra Electronics showed that the number of "Space Commander" walkie-talkies assembled by the average worker t hr after starting work at 8:00 a. m. is given by N(t) = −t3 + 6t2 + 15t for 0 ≤ t ≤ 4 How many walkie-talkies can an average worker be expected to assemble between 8:00 and 9:00 a. m.? Between 9:00 and 10:00 a. m.? 8:00 - 9:00am walkie-talkies 9:00 - 10:00am walkie-talkies