In a quadrilateral ABCD, angle A = 130 degrees, angle B = 50 degrees, angle C = 30 degrees. Find angle D.

Before finding out the value of the angle D in the quadrilateral ABCD,
it is necessary to pay attention to the rule according to which the sum of the angles of any quadrangle is 360 °.
Thus, for a given quadrilateral ABCD, the following equality can be drawn.
A + B + C + D = 360 °.
Now we substitute the corresponding numerical values of the angles A, B and C, data on the condition of the problem, and then calculate.
130 ° + 50 ° + 30 ° + D = 360 °.
210 ° + D = 360 °.
D = 360 ° – 210 °.
D = 150 °.
Answer: D = 150 °.