Assume each pair of figures is similar. Find the missing side length Pls explain I’m confused

You have to find the ratio used to turn 24 into 18 inches then use that same ratio to turn 18 inches into the answer so it would be 4:3 ratio because 24:18 simplified is 4:3 if you do the same to the side that’s originally 18 you would devise it by 4 then multiply that number by 3 to get the length on the second triangle