Choose the expression that represents a cubic expression.
a. 19x^4 + 18x^3 - 16x^2 - 12x + 1
b. 10x^3 - 6x^2 - 9x + 12
c. -9x^2 - 3x + 4
d. 4x + 3

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