FROM .......xbar = 35201, s = 2615, n = 50 ............it seems that you want to prove

where is the expected life time of these tires.

HOWEVER, the question seems to be about probabilities...

Based on the english I would say >.85" alt="H_a>.85" />

where p is the true poroprtion (probability) of tires that survive 30,000 miles.