Official solution
Distance beetween point A and B is = 14 unit
As y coordinate of point A(-8, 5) and B(6, 5) are same. So line AB is parallel to the x axis.
Point O is the center of the circle and OP is the perpendicular to the line AB. And P is the mis point of line AB.
\[ \therefore \] Point P = \[\left( {{{ - 8 + 6} \over 2},{{5 + 5} \over 2}} \right)\] = (-1, 5)
As OP is perpendicular to the line AB and AB is parallel to the x axis then OP is parallel to the y axis. So x coordinate of line OP is constant.
\[ \therefore \] x coordinate of O = -1
And point O is lies on the line 3y = x + 7
\[ \therefore \] 3y = -1 + 7
\[ \Rightarrow \] y = 2
\[ \therefore \] Center O = (-1, 2)
\[ \therefore \] OP = 3
Then BC = 2OP = 6
\[ \therefore \] Area of rectangle = (AB)(BC)
= 14 \[ \times \] 6
= 84