Answer:
7
Explanation:
Mechanical advantage is given by the ratio of the distance of the fulcrum from the two objects of the system.
Here the boulder is [tex]0.5\ \text{m}[/tex] from the fulcrum and the mass at the other end of the lever is [tex]4-0.5=3.5\ \text{m}[/tex] from the fulcrum.
So, mechanical advantage is given by
[tex]MA=\dfrac{3.5}{0.5}\\\Rightarrow MA=7[/tex]
So, mechanical advantage of the board is 7.