Let ∠APC = θ is angle between the given lines AB and CD.
The acute angle is the small angle which is less than 90°.
The obtuse angle is the smaller angle.It is more than 90° and less than 180°.
The 90° is rarely written in. A right angle can be in any orientation or rotation as long as the internal angle is 90°. If we see the box in the corner, we are being told it is a right angle.
A Reflex Angle is more than 180° but less than 360°
These two angles (40° and 50°) are Complementary Angles, because they add up to 90°. Notice that together they make a right angle.
These two angles (140° and 40°) are Supplementary Angles, because they add up to 180°. Notice that together they make a straight angle.

Let ∠APC = θ is angle between the given lines AB and CD.
Let 39 be the angle made between lines l(AB) & l(CD)
Thus ∠APC = 39 °
Since a straight line always makes 180° i.e. angles of a line are always Supplementary Angles
Since ∠APC = 39 ° thus its Supplementary Angle is ∠APD
Thus ∠APD + ∠APC = 180°
Thus ∠APD = 180° - ∠APC
Thus ∠APD = 180° - ∠39 °
Thus ∠APD = ∠141 °