$($II$)$ In a certain region of space, the electric field is

constant in direction $($say horizontal, in the $x$ direction$),$

but its magnitude decreases from $E=650\frac{N}{C}$ at $x=0$

to $E=370\frac{N}{C}$ at $x=25m.$ Determine the charge

within a cubical box of side $l=25m,$ where the box is

oriented so that four of its sides are parallel to the field

lines $($Fig$.22-29).$

FIGURE $22-29$

Problem $9.$