Let a and b be constants. If 3x^3-ax^2+5x-3b is divisible by x + 3 then 3a + b =?

∵ 3x³ - ax² + 5x - 3b is divisible by x + 3
[ It means f(-3) = 0 ]

f(-3) = 3(-3)³ - a(-3)² + 5(-3) - 3b = 0
- 81 - 9a - 15 - 3b = 0
- 96 - 9a - 3b = 0
3 (3a + b) = - 96
3a + b = - 96/3 = - 32

f(x)=3x^3-ax^2+5x-3b
x+3=0
x=-3
f(-3)=3(-3)^3-a(-3)^2+5(-3)-3b
0=-81-9a-15-3b
96=-9a-3b
-3(3a+b)=96
3a+b=-32