To find y you must recognize that 141+3y=180 . You know this since half of a circle is 180, and a line is basically half a circle if you arc from end point to end point.
You can then subtract 141 from both sides,
3y = 39
Then divide both sides by 3,
y=13
You would want to use 39° for 3y° since 3·13= 39.
A triangle can only contain 180°, so you would add 68 and 39 together and then subtract this from 180 to give you x.
