HELP! Math question! (Recursive Sequences)

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?

Rounded to the nearest tenth, what is the value of x

Alakefront cottage that is 30 feet high casts a shadow on the water. how long is that shadow if a 16-foot-high truck parked nearby casts an 8-foot shadow?