I need help on this problem, I don't get 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?

Which expression do you get when you eliminate the negative exponents of 4a^2 b^216a^-3 b

Acredit union pays 5% annual interest, compounded daily, on savings deposits. find the value after one year of $500 deposited in this account. $525.64 $25.64 $20.40 $520.40