∠1 and 105° are supplementary angles. (supplementary = 180°)
180 - 105 = 75°
∠1 = 75°
∠1 and ∠2 are corresponding angles, and so there measurements will be the same
∠1 = ∠2
∠1 = 75°
∠2 = 75°
105° and ∠3 are same side, and are corresponding angles. Therefore, ∠3 = 105°
m∠1=75°
180° (the measurement of a straight angle).
Subtract the 105° (given) from the straight angle
180 - 105 = 75
m∠1=75°
hope this helps