Answer
$x = 21$
$y = 39$
Work Step by Step
In a parallelogram, opposite angles are congruent. Let us set opposite angles equal to one another to solve for $x$ and $y$:
$3x = 4x - 21$
Subtract $4x$ from each side of the equation to move the variable to one side of the equation:
$-x = -21$
Divide each side of the equation by $-1$ to solve for $x$:
$x = 21$
Let us set the other opposite angles equal to one another to solve for $y$:
$3y = y + 78$
Subtract $y$ from each side of the equation to move the variable to the left side of the equation:
$2y = 78$
Divide each side of the equation by $2$ to solve for $y$:
$y = 39$
