To find the length of the effort arm needed to achieve a mechanical advantage of 8 with a load arm of 0.4 meters, you can use the formula for mechanical advantage (MA) in a lever:
\[ MA = \frac{\text{Effort Arm}}{\text{Load Arm}} \]
Given that the mechanical advantage (MA) is 8 and the load arm is 0.4 meters, you can rearrange the equation to solve for the effort arm:
\[ \text{Effort Arm} = MA \times \text{Load Arm} \]
Substituting the known values:
\[ \text{Effort Arm} = 8 \times 0.4 \text{ m} = 3.2 \text{ m} \]
So, Samantha should make the effort arm 3.2 meters long to achieve a mechanical advantage of 8.
The correct answer is 3.2 m.