To add or subtract some rational numbers, you have to change the rational numbers so they have a common denominator. When you have a common denominator, you can then go on with the addition or subtraction on the numerator part.
To add or subtract these rational numbers, you first need to change your rational numbers so that they share a common denominator. Once you have a common denominator, you can then go ahead with the addition or subtraction of just the numerator part
