An experiment is conducted to study the longevity of engine timing belts made of a new type of material. The experiment is run for a fixed time of 9 years. (Thus, the test is censored at 9 years. The sample results (in years) are 6.5 5.4 6.4 9+ 9+ (where 9+ indicates that the timing belt was still in tact at the end of the experiment). What can you say about the mean life span of one of these timing belts? the mean timing belt life (in years) is greater than