The correct answer is 15 N.
Step-by-step 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,
![2=(30)/(I.F)](https://img.qammunity.org/2019/formulas/physics/high-school/fsblk5qw09xmi7s4mugv3z4augz1723kxh.png)
Input force = 15 N
∴ The input force must be 15 N.