2(x +9) - 7x +4 simplify expression

Sera sells t-shirts at the beach. she believes the price of a t-shirt and the number of t-shirts sold are related. she has been experimenting with different prices for the t-shirts. she has collected a data set with five pairs of data; each consists of the price of a t-shirt and the number of shirts sold. the independent variable, which will go on the x-axis, is . the dependent variable, which will go on the y-axis, is the