7y^2-42y 7y(y - 6)
------------ = -------------
y^2-3y-54 (y - 9)(y + 6)
----------------
(y - 6)
----------
(y + 6)
to divide fraction you multiply by the reciprical (turn the bottom fraction upside down
7y(y - 6) (y + 6) 7y
------------- * --------- = ---------
(y - 9)(y + 6) (y - 6) (y - 9)