Well, the total angles in a triangle is 180 degrees.
Right now, in this triangle, we have the measurements of 70 degrees and 90 degrees so, 70 + 90 equals to 160 degrees.
So, now, if we subtract 160 from 180, we get the answer if 20 degrees.
Glad I could help and also, can you mark my answer as the brainliest answer?
Thank you so much!
