Answer:
105 degrees
Explanation:
Recall that the sum of angles in a triangle is 180 degrees. As such, where a, b and c are the angles of a triangle then
a + b + c = 180 ( all in degrees)
Given that two angles of a triangle measure 55 and 20, let the size of gthe 3rd be T then
55 + 20 + T = 180
simplify
75 + T = 180
Subtract 75 from both sides
T = 180 - 75
T = 105