B,solve the equation to find the dimension of the plot

The quadratic equation formed in part A is:

$$w^2 + 3w - 180 = 0$$

We can solve this by factoring. We need two numbers that multiply to -180 and add to 3. These numbers are 15 and -12.

$$(w + 15)(w - 12) = 0$$

This gives two possible values for $w$:

$$w + 15 = 0 \implies w = -15$$ $$w - 12 = 0 \implies w = 12$$

Since the width of a plot cannot be negative, we discard $w = -15$.
Therefore, the width of the plot is $w = \text{12 metres}$.

From the problem statement, the length is 3 metres more than the width:

$$l = w + 3$$

Substitute the value of $w = 12$ metres into this equation:

$$l = 12 + 3$$ $$l = \text{15 metres}$$

The dimensions of the plot are:
Width: $\boxed{\text{12 metres}}$
Length: $\boxed{\text{15 metres}}$