-9/7x + 8 < -4x - 5

-9/7x + 4x + 8 , -4x + 4x - 5
-9/7x + 4x +8 < -5
The book then has
19/7x + 8 < - 5
I know how to solve this but I am lacking or trying to remeber how they got 19/7 - need a refresher

Convert the "x" terms to common denominators
4 x - (9/7) x = 28 x - (9/7) x
= (19/7) x