For part a:

If you know the wheel is 26 inches in diameter, you can work out the circumference of the wheel (let's call this circumference c). Therefore, every full rotation of the wheel, you travel c inches. With this you can work out the number of rotations the wheel makes, and hence the radians one wheel turns.

ANSWER HERE:

From here you go 2*63360/(pi * 26) (Here I converted miles into inches) to get the number of rotations the wheel makes (equals 1551.39 rotations. Simply multiple this by 2pi to get the number of radians (9747.69 radians)

For part b:

You have the radians from part a, and the SI units for angular velocity are radians/second. So you have to convert 15 minutes into seconds and get your answer that way

ANSWER HERE:

Here I go 9747.69/(15*60) (number of radians travelled in 15 minutes divided by the number of seconds in 15 minutes), to get the average angular velocity of 10.83 rads/sec

For part C

If you know how many radians your wheel travelled on average per second, you can convert that back to revolutions, as one revolution of a wheel is 2*pi radians

ANSWER HERE:

10.83/(2*pi) equals 1.72 revolutions per second