a +  - 

Write a as 

 +  - 

The LCD is 12.

The denominator of  needs to be multiplied by 12 to become
the LCD of 12, so multiply the first fraction by 

 +  - 

The denominator of  needs to be multiplied by 3 to become
the LCD of 12, so multiply the second fraction by 

 +  - 

The denominator of  needs to be multiplied by 2 to become
the LCD of 12, so multiply the third fraction by 

 +  - 

Multiply the numerators and the denominators in each of the the three
terms:

 +  - 

Now that all three fractions have the same denominator, we combine
the three numerators and write that over the LCD of 12:




Combine the like terms 12a and -2a and get 10a.

So the final simplification is



Edwin