21. Find the value of x.

We have a line with the angle $$50^{\circ}$$ and $$130^{\circ}$$. If the lines are parallel, then the same-side interior angles sum to 180 degrees. Since $$50+130 = 180$$ the lines are parallel. We can compute the angle adjacent to $$70^{\circ}$$, which is $$180-70=110^{\circ}$$. Therefore we have triangle with $$55^{\circ}$$, x, and $$110^{\circ}-50^{\circ}=60^{\circ}$$. So, $$x+55+60 = 180$$, then $$x+115=180$$. Hence, $$x=180-115 = 65^{\circ}$$. **Answer: 65°**