A popular soft drink is sold in 1​-liter​(1,000​-milliliter)bottles. Because of variation in the filling​ process, bottles have a mean of 1,000 milliliters and a standard deviation of 18 ​milliliters, normally distributed. Complete parts a and b below.

a. If the process fills the bottle by more than 20 ​milliliters, the overflow will cause a machine malfunction. What is the probability of this​ occurring?