#### Answer

(34-2x) (21-2x) $=$ 600

#### Work Step by Step

The picture is surrounded by a frame from all sides, whose dimensions are, 34in $\times$ 21in.
To find the dimensions of the picture, we need to subtract the border.
Length of picture $=$ $34-x-x$
$=$ $34-2x$
Width of picture $=$ $21-x-x$
$=$ $21-2x$
Now we have the dimensions of the picture. To find the area (which in this case is given as 600 $in^{2}$), we need to multiply the length and breadth. ie,
(34-2x) (21-2x) $=$ 600
Thus the answer is option B.