Find the Area of the triangle.

Need on this geometry question. explain how you did it.

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?

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'