The properties of a rhombus is such that all four sides are equal. And, a rhombus is a parallelogram. |dw:1443027899761:dw| Hence the angles BAC and BCA are congruent because AB=BC. Can you take it from here?
can you continue the steps?
If the angles BAC and BCA are congruent , then 2x+39=6x-9 solve for x.