a. 80/360 degrees= 8/36=2/9. Then the arc length of PQ must be 2/9 the circumference. The circumference is 2(pi)(10)=20pi. Then the arc lenght is 2/9*20pi=40/9pi.
b. The area must be 2/9 the total area. The area of the circle is 10^2pi=100pi. So the area of the sector formed by POQ is 2/9*100pi=200/9pi.