HElp me pls.?

Question

A uniform horizontal line of a matter is l=56,000 km long, and has mass M = 3.6 *10^5 kg. What is the (vector) gravitational force due to the line on a particle of mass m=25 kg located x= 20,000 km to the right? PLease do the problem and write the answer for unknown value of l, M, m and x -and any constants you except for small integers. only at the end substitute the numbers in for the letters.;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

problem 2 ( which is related)
What is the gravitational potential energy of the particle in the previous problem? ( if the particle is an infinite distance away, the potential enery is zero)
The second paragraph of the previous problem applies here.

Answer 1

It is analogous to an electric line of charge (see ref 1)

F= [G m (M/L)/d] [ b/sqrt(d^2 + b^2) + a/sqrt(d^2 + a^2)]

F- force in question
G- gravitational constant
m- mass of object as given (26kg)
M - mass of the line mass
L- length of the line mass
b - distance to the right (your x)
a - distance to the left
d - perpendicular distance from mass m to line mass M.

So what is d?

Problem 2

P= Fd
F= GmM/d^2
P=(GmM/d^2)d
P= GmM/d
so as d-> infinity
P -> zero.