The measures of the interior angles of a quadrilateral add up to 360 degrees, so make angles A, B, C, and x add up to 360 in an equation and solve for x, the missing angle.
(80) + (98) + (70) + x = 360
Combine like terms.
248 + x = 360
Subtract 248 from both sides.
x = 112
C) 112 degrees
You can plug -x - 1 for y in the first equation
2x - (-x - 1) = 10
2x + x + 1 = 10
Combine
3x = 9
Divide
x = 3
Plug 3 for x in any equation ( I'll use th second equation )
y = - (3) - 1
y = - 3 - 1 = -4
x = 3 ; y = -4
(3, -4)
To the nearest would be about 52
