To factor this, we find factors of a·c that sum to b; this means factors of 3(20) = 60 that sum to -19:
60 = 1(60) or -1(-60); 2(30) or -2(-30); 3(20) or -3(-20); 4(15) or -4(-15); 5(12) or -5(-12); 6(10) or -6(-10). The only of these that sum to -19 are -4 and -15. This means we will split up -19x into -4x and -15x:
3x²-4x-15x+20
Next we group the first two terms and the last two terms:
(3x²-4x)+(-15x+20)
Factor out the GCF of each group. For the first group, this is x:
