Answer
$x = 5$
Work Step by Step
Parallelograms have opposite sides that are congruent. In order for $ABCD$ to be a parallelogram, we must have $AB$ and $CD$ equal to one another.
$AB = CD$
Let's plug in what we are given in the diagram:
$5x - 8 = 2x + 7$
Add $8$ to each side of the equation to isolate variables on one side of the equation:
$5x = 2x + 15$
Subtract $2x$ from each side of the equation to isolate the variable on the left side of the equation:
$3x = 15$
Divide each side of the equation by $3$ to solve for $x$:
$x = 5$
