Jackie, there are a number of ways to solve this. Since 6 is half of 12, you need half of 1 1/4. How can we find that?
1 1/4 = 5/4. To get half a feaction, double the denominator. You should know, for example, that 1/4 is half of 1/2.
So, half of 5/4 is 5/8. You need 5/8 of a cup of water.