<O = 16 degrees vertical angles are equal
<O + 4x+90 = 180 DC is a straight line
16 +4x +90 = 180
106 +4x = 180
4x =74
x =18.5
16 +90 +2y= 180 DC is a straight line
106+2y=180
2y = 74
y= 37
Answer : y=37
x=18.5
Answer:

Try to solve the similtanious equation to find the first term and the common difference, then use that information to figure out the 80th term... Update me if you need further help ...
The constant of proportionality is 13