Find the missing angle

In parallelogram ABCD, AC is a diagonal, the measure of ∠ABC is 40°, and the measure of ∠ACD is 57°.  What is the
measure of ∠CAD?

A.)  40°
B.)  57°
C.)  77°
D.)  83°
E.)  97°

​Since ∠ABC is 40°, then ∠ADC is also 40°.

Subtract 57° and 40° from 180, and that will be the measure of ∠CAD, because angles of a triangle add up to 180°.

180 - (57 + 40)  {subtracted the two known angles of the triangle from 180}
= 180 - 97
= 83  

D.)  83°

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