Answer:The correct answer is option D.
Explanation;
Ideal mechanical advantage is defined as ratio of force exerted by the machine to the force applied on the machine.
[tex]I.M.A=\frac{Force_{out}}{Force_{in}}[/tex]
[tex]I.M.A=4=\frac{Force_{out}}{6.0 N}[/tex]
Output force = 24 Newtons
Hence,the correct answer is option D.