Factorise the expression 6x2 + 11x + 4.

To factorise the quadratic expression $ax^2 + bx + c$, we look for two numbers that multiply to $a \times c$ and add up to $b$.
Here, $a=6$, $b=11$, $c=4$. So, we need two numbers that multiply to $6 \times 4 = 24$ and add up to 11. These numbers are 3 and 8.
We rewrite the middle term $11x$ as $3x + 8x$.

Now, we factor by grouping.

Factor out the common binomial $(2x + 1)$.

The factorised expression is $\boxed{(3x + 4)(2x + 1)}$.

The area of a rectangle is given by length $\times$ width. Since the area is represented by the expression $6x^2 + 11x + 4$, and we factorised it into $(3x + 4)(2x + 1)$, the dimensions are the factors.
The dimensions of the garden are $\boxed{3x + 4}$ and $\boxed{2x + 1}$.

Substitute $x = 2$ into the expressions for the dimensions:
Length: $3(2) + 4 = 6 + 4 = 10$ metres.
Width: $2(2) + 1 = 4 + 1 = 5$ metres.
The actual dimensions are $\boxed{10 \text{ metres}}$ and $\boxed{5 \text{ metres}}$.

Now, calculate the actual area:
Area = Length $\times$ Width = $10 \text{ m} \times 5 \text{ m} = 50 \text{ m}^2$.
The actual area of the garden is $\boxed{50 \text{ m}^2}$.

Factorisation is useful because it allows us to break down a complex expression (like the total area) into its simpler components (like the length and width of the garden). This helps in understanding the individual parts of a problem, which is essential for planning, design, and making practical calculations in real-world scenarios.