Carbon-11 has a radioactive half life approximately 20 mins and is useful as a diagnostic tool in certain medical applications determine (a) so that a(t) = aoat where (t) is time

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?