I need an explanation for this

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?

Solve the equation by completing the square. x^2+2x=17

Cone a has a surface area of 384 ft2 and cone b has a surface area of 96 ft? . what is the ratio of their volume?