Imagine first splitting 6 wholes up into fourths. That means that, for each whole (each 1) in 6, we're creating 4 equal slices. This gives us 4 x 6 = 24 total slices, which we call fourths. How many groups of 3 fourths (3/4) can you make out of those 24 fourths (24/4)? If we throw aside the label fourths for a minute, in general, if we have 24 things, how many groups of 3 things can we make out of those? Well, our answer there would just be 24 ÷ 3 = 8 groups.
The same thing applies to fourths. If we have 24/4, and we divide it by 3/4, we get 24 ÷ 3 = 8 groups again, so our answer is 8 3/4-pound packages.