Can someone please help.

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?

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?

Including 6% sales tax, an inn charges $135.68 per night. find the inns nightly cost