If a, b, c, and d are four different digits from 1 to 9, inclusive, then what's the largest possible value for the decimal a. b + c. d ?

Amanufacturer knows that their items have a normally distributed lifespan, with a mean if 9.1 years, and standard deviation of 2.9 years. if you randomly purchase one item, what is the probability it will last longer than 10 years?