Yeah lol I just got a guest answering like that

"the answer is 18"

Like.... ok i guess?

Btw: (I'm not bothering with latex :p )

If your load is x, and one of your neighbors trucks can carry y,

Then we have:

x >= y+600

x <= 1/3(4y)

y+600 <= x <= 1/3(4y)

If we equate y+600 = 1/3(4y), we get y=1800 (the max value for y)

And our upperbound (1/3(4y)) is 2400

The greatest load your truck can carry is 2400 pounds :]

(If that is incorrect, I think there is no real solution, all values of x and y will satisfy this equation.)