Finding angular speed/accel from tangential speed

[thatgirlyouknow]

Homework Statement

Professional recording studios often use reel-to-reel tape decks. On such a tape deck, the tape is pulled past the playback head at a constant linear speed of 0.381 m/s. (a) Using the data in part a of the figure, find the angular speed of the take-up reel. (b) After 2.79 x 10^3 s, the take-up reel is almost full, as part b of the drawing indicates. Find the average angular acceleration of the reel with the appropriate sign, where a positive value means the reel is speeding up.

Homework Equations

Vtangential = r*omega (which here will be w)
accelerationtangential = r*alpha (here,alp)

The Attempt at a Solution

.381 m/s = r * w rad/s

In the diagram, r isn't given. Is there a way I can find it? It's constantly changing because of the tape's reeling effect, so I'm not sure how that would fit in.

 

[haruspex]

In the diagram, r isn't given

making the question unsolvable.