Answer:
16
Step-by-step explanation:
Subtracting the 2 expressions
3b² - 8 - b(b² + b - 7) ← distribute parenthesis
= 3b² - 8 - (b³ + b² - 7b) ← distribute parenthesis by - 1
= 3b² - 8 - b³ - b² + 7b ← collect like terms
= - b³ + 2b² + 7b - 8 ← substitute b = - 3 into the expression
= - (- 3)³ + 2(- 3)² + 7(- 3) - 8
= - (- 27) + 2(9) - 21 - 8
= 27 + 18 - 21 - 8
= 16
