A 30 ft by 40 ft classroom with 8 ft high ceilings will have an ambient lighting target illuminance of 70 fc at a work plane that is 28 in. above the floor. It is anticipated that the ceiling reflectance is 0.5 and the average wall reflectance is about 0.3. The space will be illuminated with recessed lay-in 2 ft x 4 ft open troffer luminaires with four lamps. The initial output of the fluorescent lamps is 2850 lumen. The light loss factor will be assumed to be 0.7. Use the zonal cavity method to determine the minimum number of luminaires required to provide uniform illumination in the space.