Since ABCD is a parallelogram, line AB and line DC are parallel and has the same value.
To solve this, equate line AB to be equal with line DC.
So,
Line AB = Line DC
(9x-14)in = (3x +4)in
Next group like terms to get the value of x
9x in-3x in = 4in+14in
= 
x = 3in
Since, we now have the value of x, substitute it to line DC’s equation.
DC=(3x+4)in
DC=(3(3) +4)in
DC=(9 +4) in
DC= 13 in
To check if the value is really correct, substitute X to AB
AB=(9x -14)in
AB=(9(3)-14)in
AB=(27-14)in
AB=13 in
To solve this, equate line AB to be equal with line DC.
So,
Line AB = Line DC
(9x-14)in = (3x +4)in
Next group like terms to get the value of x
9x in-3x in = 4in+14in
x = 3in
Since, we now have the value of x, substitute it to line DC’s equation.
DC=(3x+4)in
DC=(3(3) +4)in
DC=(9 +4) in
DC= 13 in
To check if the value is really correct, substitute X to AB
AB=(9x -14)in
AB=(9(3)-14)in
AB=(27-14)in
AB=13 in