What concepts do you think belong in this branch of mathematics?

If i have one apple and give you the apple, how many apples do i have?

What is the range for 31,39,29,34,37,24,36,33,34,28

Lin is writing an equation to model the proportional relationship between y, the total cost in dollars of downloading videos from a website, and x, the number of videos downloaded. she knows that the total cost to download 3 videos was $12. her work to find the equation is shown below. joylin’s work step 1 k= 3/12= 0.25 step 2 y= 0.25x where did joylin make her first error?