Answers

2014-06-20T12:57:42+05:30
Let the 4 angles be (a-3d),a-d,a+d,a+3d
sum of all the angles in the quadrilateral=360
so a-3d+a-d+a+d+a+3d=4a=360
a=90
but the angles are a-3d=a-30=90-30=60 as d=10
a-d=90-10=80
a+d=100
a=3d=120 

1 5 1
your answer is wrong as d = 10 is given.
i also used d=10 see the 4th step from last