Question

Can someone give me their opinion on whether or not I'm right?

The lifetime of a 2-volt non-rechargeable battery in constant use has a Normal distribution with a mean of 516 hours and a standard deviation of 20 hours. Ninety percent of all batteries have a lifetime less than
A. 517.28 hours.
B. 536.00 hours.
C. 541.60 hours.

I said it was 536 since 556 isn't there which was my first choice...