Hey there!
If our central angle is 77, our arc on the outside that it intercepts is going to be 77/360 of the total circumference of the arc. This is because a full circle angle is 360 degrees, so if our central angle was 360, we would just find the circumference of the circle as the arc would be the entire circle.
In our case, we will just find the circumference and then multiply it by 77/360 to find our arc length as we are just looking for a fraction of our total circle.
Circumference is 2πr, so we have 2π(6)≈37.68
Now we multiply this by 77/360.
37.68×77/360≈ 8.06
So now, if you have a radius r and a central angle x, you can use the formula x/360 ×2πr to find the arc length.
Have a wonderful day! :D