You know that the two angles on the longer sides must add to 180 degrees.
3x+5+70=180
3x+75=180
3x=105
X=35 degrees
So you've got x, now plug it into the other angle that you can determine.
2x
2(35)=70
Now you can use the previous strategy for the last angle
70+x+3y=180
70+35+3y=180
3y=75
Y=25 degrees
There you go, you've got x=35 and y=25
