Calculating Rotational Speed for Wheel C: 240.7 rev/min

[hatingphysics]

Wheel A of radius ra = 14.6 cm is coupled by belt B to wheel C of radius rc = 28.8 cm. Wheel A increases its angular speed from rest at time t = 0 s at a uniform rate of 7.1 rad/s2. At what time will wheel C reach a rotational speed of 240.7 rev/min, assuming the belt does not slip?

I did ...Vta = Vtc, but stil didint get it. i got the Vtc
value and divided that by raduis of A to get w for a. then
divided the acceleration by the w for a, but my time is
still wrong!

 

[berkeman]

Sounds like you are basically using the correct approach. Can you please post your calculations (including units) so we can see if it's just a math error?