The angular position of a point on the rim of a 45.8 cm rotating wheel is given by θ(t) = 3.6 t2 − 2.8 t +7.5,

What is the instantaneous speed v of the point at time t = 6.5 s?

I assume you are in calculus.

d Theta/dt=w=7.2t-2.8

then at that point, speed=wr