Help solving this math

The hour hand makes a full circle of 12 hr, in 45 min=0.75 hours it will will have made 0.75/12 of a full circle. Given that the tip of the hour hand travels along the circumference of a circle, the radius of circle will be equal to the lenth of the hand. 
But:
circumference is given by:
C=2*π*radius
The distance traveled by the hand in 12 hours will be:
2**36=76π mm
The distance traveled in 45 min will be:
0.75/12 *72π=4.5π mm
in 45min, the min hand will make 45/60=3/4 of a full circle. If the min hand is 150% of the hour hand, then its length is 150/100*36=54 mm.
Thus the tip of the minute will travel along the entire circuference of a circle with a 54 mm radius, this implies that for a full circle we shall have:
2*π*54mm=108π mm.
Hence;
in 45 min, the tip of the minute hand will have traveled 108*3/4*π=81π mm