As we know that sphere roll without slipping so there is no loss of energy in this case
so here we can say that total energy is conserved
Initial Kinetic energy + initial potential energy = final kinetic energy + final potential energy

as we know that ball start from rest

height of the ball initially is given as


also we know that

also for pure rolling

also we know that


now plug in all data in above equation




So speed at the bottom of the inclined plane will be 29 rad/s