Jika P = 7a - 8b - c dan Q = -3a + 2b - 6c, hasil dari P - 2Q adalah Please help me,,,,

P = 7a-8b-c
Q = -3a+2b-6c
P-2Q = 7a-8b-c-2 (-3a+2b-6c)
= 7a-8b-c+6a-4b+12c
= 7a+6a-8b-4b-c+12c
= 13a-12b+11c