1 .NEED HELP ASAP WILL GIVE

How do you use the additive inverse to evaluate an expression that uses subtraction in a full sentence

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

Mozart lenses inc. recently introduced seelites, a thinner lens for eyelasses. of a sample of 800 eyeglass wearers, 246 said they would purchases their next pair of eyeglasses with the new lenses. lenses inc. estimates that the number of people who purchase eyeglasses in a year is 1,700,000. most eyeglasses wearer buy one new pair of eyeglasses a year. what is the annual sales potential for the new lenses.