I think the answer would be 0.16

Here, in the given figure. Angle y° forms vertical opposite angle pair with Angle 163°, therefore they have equal values.
that means ~

For sake of convenience, reverse the series, then it would be:
21,19,17.....7
a=21, d = -2,
s(4) = 4/2 (21+15)
s(4)=2(36)
s(4) = 72
The GCF is 2
Pull out 2 from each number:
2(2n + 5)
Hope this helps!
I'm not sure but I'm gonna guess that the answer is 50?