Question

What is the value of X if the quadrilateral is a rhombus?

Answer 1

Since all the sides of a rhombus are equal you have to let 15= 4x+3 so it will proceed like this:

15=4x+3
(Subtract 3 from each side)
12=4x
(Divide each side by 4 to isolate the variable, x)
x=3

Hope this explanation helps ;)