How do i factor this expression

1/8x^2 - 13/168x - 5/42

one eighth xsquared - thirteen over one hundred sixy eight x - 5/42

thank you ;( ten points

(1/8) x^2 - (13/168) x - 5/42

8 = 2^3
168 = 4 • 42 = 2^3 • 6 • 7
42 = 6 • 7 = 2 • 3 • 7

LCM = 2^3 • 6 • 7 = 168

(21/168) x^2 - (13/168) x - 20/168 = (21x^2 - 13x - 20)/168 = (3x - 4)(7x + 5)/168