Here's the question you clicked on:
marcoduuuh
What is the length of PR? (Picture below.)
25+114 to figure out that side?
okay you know that the big triangle has the length of DE as 15units and the little triangle has the length of the corresponding side as 5units, so how did you get from 15 to 5? you divide by 3. so you would do the same for side DF since it corresponds with side PR or x. so divide 21 by 3 and get x! tah dah! yay math! jk
same as saying set up as a ratio 15/5=21/x or x/5=21/15
Best explanation I've ever had. Omg, tah dah. Thank you so much <33