Question

Abcd is a quadrilateral
Angle ,a=50
B= 100
C=70
D=

Answer 1

By angle sum property of quadrilateral
Angle A+ B+C+D = 360
50+100+70+D = 360
220+D = 360
D= 360-220
D= 140

Answer 2

$d = 120 \\ \\ because \: we \: know \: that \: the \: sum \: of \: all \: side \: of \: quadrilateral \: is \: 360 \\ \\ so. < a + < b + < \: c + < d = 360 \\ \\ \\ = > 100 + 70 + 50 + d = 360 \\ \\d = 360 - 220 = 120$