Finding arc length without radius

Question

Hello geniuses of the math-ternet, a 10th grade student I tutor in math showed me this exam question (ignore the scribblings). It asks for the arc length of RST, even though no radius, circumference, or any measure of length is given, only an angle. I'm stumped. How do you solve for an arc length with no unit / length to reference? Am I missing something obvious? Thanks in advance.

Edit: It's unlikely that the teacher "missed" a variable because on the same test, this question was also asked. It's the same as the first question, just asking for angle from arc length this time.

Answer 1

Accordding to wikipedia (https://en.wikipedia.org/wiki/Inscribed_angle) or actually the theorem about the inscribed angle, the arc RT must be twice as big as the given $52^°$. We therefore calculate: $2\cdot 52^° = \frac{104^° \cdot 2\pi}{360^°}$, which is equal to $\frac{26}{45} \pi$. Subtracting it from $2 \pi$ yields $\frac{64}{45} \pi$, therefore A) is the correct answer.

Answer 2

It doesn't actually say arc length but rather arc measure, which is simply the angle measure if you connected the two points on the circle to the center in radians, so convert to radians and use inscribed angle to solve for that angle.

The answer by user1047209 explains that. (Sorry for the lack of a diagram I don't actually know how to add one...but the main point is just that its the angle, not length, so no measurement of length is necessary)

Edit: in the second link you sent the teacher is straight up wrong (I think I'm only in high school too though), radians are not a measure of length, so arc length can't be in radians