To find the base of a right triangle when you know the area and the height, you can use the formula for the area of a triangle:
\[ \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} \]
In this case, you are given:
- Area = 33 mm²
- Height = 11 mm
Plugging these values into the formula gives:
\[ 33 = \frac{1}{2} \times \text{base} \times 11 \]
To solve for the base, first multiply both sides of the equation by 2:
\[ 66 = \text{base} \times 11 \]
Next, divide both sides by 11:
\[ \text{base} = \frac{66}{11} = 6 \text{ mm} \]
Thus, the length of the base of the triangle is:
\[ \boxed{6} \text{ mm} \]