y = 90°
Solution:
The reference image for the answer is attached below.
The sum of opposite interior angles is equal to the exterior angles.
m∠BAC + m∠ACB = 110°
m∠BAC + 70° = 110°
m∠BAC = 110° – 70°
m∠BAC = 40°
m∠BAD + m∠DAC = 40°
x + x = 40°
2x = 40°
Divide by 2 on both sides of the equation.
x = 20°
In triangle DAC,
Sum of all the angles of a triangle = 180°
m∠DAC + m∠ACD + m∠CDA = 180°
20° + 70° + m∠CDA = 180°
90° + m∠CDA = 180°
m∠CDA = 180° – 90°
m∠CDA = 90°
∠CDA and y lies on the straight line. So they form a linear pair.
y + m∠CDA = 180°
y + 90° = 180°
y = 180° – 90°
y = 90°
The value of y is 90°.