Answer:
The force will be 54.0 units
Explanation:
The magnitude of the electrostatic force between two charged objects is given by Coulomb's Law:

where
k is Coulomb's constant
q1, q2 are the magnitude of the two charges
r is the separation between the two charges
From the equation, we see that the magnitude of the force is directly proportional to the charge of object 2:

In this problem, the initial force between the two objects is
F = 18.0 N
And so, when the charge on object 2 is tripled,

The new electrostatic force will be

So, the force will also triple: since the original force was 18.0 units, the new force will be

Answer:
(C) length / height of the plane
Explanation:
The mechanical advantage of an inclined plane can be determined using different variables. In this case, the geometry of the setup is relevant. The advantage is proportional to the length of the plane, and inversely proportional to the height: it is the ratio (length) / (height) of the plane. For example, given a desired, fixed height, a long inclined plane gives you a bigger mechanical advantage than a short inclined plane. In this example, pushing an object up the long plane will require a smaller force, than it would on the short plane.
Strictly speaking, (D) would also "allow you to determine the mechanical advantage" because you could simply invert the ratio listed under (D). However, (C) is the best, direct, answer.