Factor Completely: 
7h³ - 35h² - 42h

First factor out 7h

7h(h² - 5h - 6)

Think of two positive integers whose product is 6 and
whose difference is 5.  They are 6 and 1. Write this:

7h(h   6)(h   1)

Since the -5h is negative, put a negative sign on the
larger, 6, and the opposite sign (positive) on the 1.

7h(h - 6)(h + 1)

Edwin