can someone please help me answer this? i will mark you brainliest!!! i really need help plss

Answer:
3.5
Step-by-step explanation:
If you get more like this just divide the big triangle to the small one. on the same lengths. Example: on this one do 14/4 = 3.5, 10.5/3 = 3.5, 21/6 = 3.5
Hope this helps! :)