21) 2x+16=2*23+16=46+16=62
3x-7=3*23-7=69-7=62,
so we can see that 2x+16=3x-7, that means that lines are parallel , because the corresponding angles are equal.
problem with triangle
130+a=180, a=50,
50+8x+2x=180
50+10x=180
10x=130
x=13
8x+b=180
b=180-8x=180-8*13=76
2x+c=180
c=180-2x
c=180-2*13= 154