Question

#19. Given a regular octagon, find the measures of the angles formed by (a) two consecutive radii and (b) a radius and a side of the polygon.

Answer 1

A regular octagon forms 8 congruent isosceles triangles, where the central angles are 360/8° or 45° each.

Your second part cannot be answered since you gave no data.
Let the radius be r and consider one of the triangles..
If the base is 2s, then
s/r = sin 67.5°
s = r sin 67.5°

and 2s = 2r sin 67.5°

So for any given radius, you can find the side, and for any given side, you can find the radius using the above relationship

Answer 2

thx @Reiny