hannah is purchasing x t-shirts that cost $13.50 each before tax. the function g(x) = 13.5x models the cost to purchase x t-shirts. the function f(x) = 0.25(13.6x) models the discount that will be applied to the cost of x t-shirts. what is the value of k if the function m(x) = kx represents the cost of x t-shirts after the discount but before tax?