b) 6а – [b + 3а – (4a – b)].
b) 6а – [b + 3а – (4a – b)].
b) 6а – [b + 3а – (4a – b)]
= 6a – [b + 3a – 4a + b]
= 6a – [2b – a]
= 6a – 2b + a
= 7a ‒ 2b.