6.23

T_avg_seek = 4ms

T_avg_rotation = 1/2 * 1/15000 * 60s/min * 1000ms/s = 2ms

T_avg_transfer = 1/15000 * 1/800 * 60s/min * 1000ms/s = 0.005ms

so

T_access = 6.005ms