First, you want to make both of the fractions have the same denominator
3/4 - 1/3
The lowest common multiple of 4 and 3 is 12
To get from 4 to 12, we multiply by 3 - therefore we must do the same to the numerator
3 x 3 = 9
3/4 → 9/12
To get from 3 to 12, we multiply by 4 - therefore we do the same to the numerator
1 x 4 = 4
1/3 → 4/12
9/12 - 4/12
Now that the denominators are the same, we can just subtract the numerators
9 - 4 = 5
5/12 pounds of salami