Pls help I'll give 20 points!

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?

Answer for 10 points show work you guys in advanced < 3

Use the quadratic function to predict f(x) if x equals 8. f(x) = 25x2 − 28x + 585