A circle is 360°.
Add the known angle measures and subtract the total from 360°.
115+105+60 =280°
360 - 280 = 80°
X= 80°
You need three non-collinear points to name a plane.
Non-collinear means "not on the same straight line". So these three points can't all lie on the same straight line. If three points do lie on the same straight line, then it is impossible to generate a single unique plane.
The expression will look like this. (3*6)+4
Ooo I don’t speak that language