The correct answer is 15 N.
Explanation:
The mechanical advantage of a machine is calculated as,
M.A = Output Force/ Input Force
Given, mechanical advantage=2
Output force = 30 N
Substituting the values,
[tex] 2=\frac{30}{I.F} [/tex]
Input force = 15 N
∴ The input force must be 15 N.