2/3
1) To find that out, we need to divide that 1/2 cup serving by 3/4 cup of a yogurt

When dividing fractions multiply the first by the reciprocate of the second one.
2) So, simplifying that 4/6 of the whole we can write
In a 3/4 cup of yogurt, there is 2/3 of 1/2 cup.