homework and exercises - How does the Moon cause the tides?

I am considering the following question, but I can't quite figure it out...

I have looked up differential gravity, but I cannot derive the equation for the effect on Earth, and I haven't found any good links for it. I have seen this question, but it doesn't seem to derive the forces on different parts of the Earth, or how the force variation affects the water. I initially tried to consider the component of the gravitational force of the Moon acting normally to the Earth's surface. This would be $F = F_0 \cos(\theta)$ where $\theta$ is the angle between a horizontal line going through $A$ and $B$ and the point on the Earth's surface in question. But now I am stuck. I wanted to deal with forces rather than equipotentials, as it seems like that is what the question wants because of the 'hence'...

How do I start with any method, be it equipotentials or forces?