as you already know, a direct proportional variation has a constant of variation "k", y = kx, which in this case that'd be the slope, namely 15.
The unknown digit is 7 because 6.471 is greater than 6.470 and less than 6.48.
For this case we have the following angle:
theta = (9/5) pi
Having the conversion we have:
theta = ((9/5) pi) * (180 / pi)
Rewriting we have:
theta = (9/5) * (180)
theta = (9/5) * (180)
theta = 324 degrees
Answer:
The angle is equivalent to:
theta = 324 degrees
3 times 7= 21 times three =63