Suppose you have D12000 to save . You have to save some amount at 10% and the rest at 15% how much should be saved at each rate to yield 12% on the total amount saved

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?