The Environmental Protection Agency requires that the exhaust of each model of motor vehicle be tested for the level of several pollutants. The level of oxides of nitrogen (NOX) in the exhaust of one light truck model was found to vary among individual trucks according to a normal distribution with mean 1.5 grams per mile driven and standard deviation 0.40 grams per mile.

What percent of trucks of this model have more than 1.15 grams of NOX in their exhaust?

I am coming up with 18.9% used standard normal distribution formula to get z score of -.88