What is a common denominator for 5/12 and 2/9

The formula for the lateral area of a right cone is la = rs, where r is the radius of the base and s is the slant height of the cone. which are equivalent equations?

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?

Having a hard time understanding this question (see attachment).