the first thing you need to do is give common denominators.
you need to find a number that the denominators have in common.
in this case it would be 12 because 4 and 6 can both go into 12
what you do to the bottom you must also do to the top.
4 *3 = 12 so you need to multiply the top by 3 as well. 3*3= 9
6*2=12 so you need to multiply the top by 2 as well 1*2=2
now we have 12 9/12 - 6 2/12
now you subtract across, 9-2= 7 and you leave the denominator the same.
12-6=6
final answer is 6 7/12
you are not able to simplify it any further