Circumference is found with the formula
c = pi × d
d is diameter and we will use 3.14 for pi.
The diameter is the measure across the center of the circle. In the first problem, you are given the radius, so we have to multiply by 2 to get the diameter. Then we can use the formula.
12.4 in × 2 = 24.8 in (that's the diameter)
c = pi × D
c = 3.14 × 24.8
c = 77.872 inches
circumference is 77.872 inches.
Try the other problems on your own. They are just like this one. Just make sure they are giving you the diameter and not the radius. Post if you have problems.
Answer:

Step-by-step explanation:
The angle marks mean those angles have the same measure. That means the sides opposite them have the same measure, so ...
2x -24 = x -2
x = 22 . . . . . . . . . add 24-x
The length of BC is x, so is 22.
BC = 22