Find the lowest common denominator for the set of fractions: 6/a^2-7a+6 and 3/a^2-36

For the answer to the question above, I'll show you the step by step.
6/a^2-7a+6, 3/a^2-36 
= 6 / (a²-7a+6) + 3 / (a² - 36) ← (uses) 
multiplying the Denominator → (a²-7a+6)(a² - 36) ← LCD 

= 6(a² - 36) / (a²-7a+6)(a² - 36) + 3(a²-7a+6) / (a²-7a+6)(a² - 36) 
= [6(a² - 36) + 3(a²-7a+6)] / (a²-7a+6)(a² - 36) 
= [6a² - 216 + 3a² - 21a +18)] / (a²-7a+6)(a² - 36) 
The answer is
= [9a² - 21a - 198] / (a²-7a+6)(a² - 36)
I hope my naswer helped you.