## Geometry: Common Core (15th Edition)

$a = 20$
We are given that the diagram is that of a parallelogram. Opposite angles of a parallelogram are congruent. We can set the two opposite angles equal to one another: $6a + 10 = 130$ Subtract $10$ from each side of the equation to isolate constants to one side of the equation: $6a = 120$ Divide both sides of the equation by $6$ to solve for $a$: $a = 20$