{40x+30( 10-x)≥340

16x+20( 10-x)≥ 170，

Solve, get

4≤x≤7.5。

And x is an integer,

∴x=4 or 567 years old.

* * * There are four schemes:

① There are 4 vehicles in A and 6 vehicles in B;

② 5 vehicles in Area A and 5 vehicles in Area B;

③ 6 vehicles in Area A and 4 vehicles in Area B;

(4) A has 7 vehicles and B has 3 vehicles.

After the first question, let the rent be W yuan, and W = 2000 x+1800 (10-x) is arranged as W=200X+ 18000, so W is a linear function of X, and the proportional coefficient is 200 and greater than 0, so W increases with the increase of X.