Answer: 15
Step-by-step explanation: Easy way to do it is of you just list all the factors and find the highest common factor, 15= 1,3,5,15. 60= 1,2,3,4,5,6,10,12,15,30,60.
The common factors here are 3 and 15 the highest common factor is 15.
Now another method is to draw the division diagrams which are shown in the image below...