Answer:
60°
Explanation:
You want the measure of angle ADC in kite ABCD with A = 2a+30°, B = a-10°, C = a, and D = B.
Sum of angles
The sum of the angles of the kite is 360°, so we have ...
A +B +C +D = 360°
A +2B +C = 360°
(2a+30°) +2(a-10°) +a = 360°
Solution
5a +10° = 360° . . . . . . collect terms
5a = 350° . . . . . . . . subtract 10°
a = 70° . . . . . . . . divide by 5
Angle D is ...
D = a-10° = 70°- 10° = 60°
Angle ADC is 60°.
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