Answer:
103°
Step-by-step explanation:
Consider triangle with angles 2, 3 and supplementary angele to angle 1.
In this triangle, angles 2 and 3 are interior angles, angle 1 is exterior angle opposit to two given interior angles.
Exterior Angle Theorem: The exterior angle of the triangle is equal to the sum of the two opposite interior angles.
Since
[tex]m\angle 2=31^{\circ}\\ \\m\angle 3=72^{\circ},[/tex]
by exterior angle theorem
[tex]m\angle 1=m\angle 2+m\angle 3\\ \\m\angle 1=31^{\circ}+72^{\circ}\\ \\m\angle 1=103^{\circ}[/tex]
