A tech conducts a study to measure the difference in how people under thirty and those thirty and over utilize their phones. They find 30 out of 150 of those under thirty and 77 out of 160 of those thirty and over use their phones primarily for phone calls.

Construct a 99% confidence interval for the difference between the proportion of those under thirty who use their cell phones primarily for making calls and the proportion of those thirty and over who do so.