Respuesta :

B. Because if you add 10+9=19, that's the side of a small side, so it wouldn't make since if you chose A. right? and it can't be D. because that's too high
The answer will be A.4, saying that the units 10 and 9 had to be added then subtracted by 15. 

Hope this helps :)
  Brainliest please.