Answer:
A - 19.5
Explanation:
A Rhombus is characterized by the diagonals meeting at a right angle. Therefore, the angle in the center is 90 degrees.
If you look at the bottom triangle, you know that the angles of a triangle add up to 180 degrees. You can say that all of the angles of the triangle added to 180 are:
(3x + 12) + (x) +(90) = 180 degrees
4x + 102 = 180 degrees combining like terms
4x + 102 - 102 = 180 - 102
4x = 78
4x/4 = 78/4
x = 19.5 degrees