Let's try this using the method I posted in your other thread.

Mulitply 6 and -15: -90

Now list all pairs of factors of -90:

1, -90

2, -45

3, -30

6, -15

9, -10

10, -9

15, -6

30, -3

45, -2

90, -1

Now which of these pairs add to 1? The 10 and -9, of course. So 1 = 10 - 9:

So set each factor equal to 0:

or

-Dan