Answer:
approximately 21, when rounded to nearest tenth.
Explanation:
First, let's find the measure of angle BAD. Angles BAD and DAC add up to 180 degrees, so 180-57= 123 degrees. Now, let's find the circumference of the circle. The circumference is diameter * π, which is 19.6(π). Then, the ratio is 123/360, so multiply 19.6(π) by 123/360, and you get 21.0381988...... which simplifies to 21 (rounded to nearest tenth)