Please solve this question and the anwers should be in English

When $P(x)$ is divided by $(x+3)$, the remainder is 18. This means $P(-3) = 18$.
Substitute $x = -3$ into $P(x) = 2x^3 + ax^2 + bx - 12$:

Divide by 3:

Given that $(x+1)$ is a factor of $P(x)$, this means $P(-1) = 0$.
Substitute $x = -1$ into $P(x) = 2x^3 + ax^2 + bx - 12$:

We have two equations:

1. $3a - b = 28$
2. $a - b = 14$

Subtract equation (**) from equation (*):

Substitute $a = 7$ into equation (**):

The values of the constants are $\boxed{a=7, b=-7}$.

Since $(x+1)$ is a factor, we divide by $x = -1$.

-1 | 2   7   -7   -12
   |     -2  -5    12
   ------------------
     2   5  -12     0

The quotient is $2x^2 + 5x - 12$.
So, $P(x) = (x+1)(2x^2 + 5x - 12)$.

We look for two numbers that multiply to $2 \times (-12) = -24$ and add up to 5. These numbers are 8 and $-3$.

The complete factorisation is $\boxed{(x+1)(2x-3)(x+4)}$.