In the diagram below, is circumscribed about quadrilateral ABCD . What is the value of ?

Answer:
C
Step-by-step explanation:
There's a property of cyclis quadrilaterals that say that opposite sides will add up to 180
so we have
[tex]5x+75=180\\\\5x=180-75\\\\5x=105\\\\x=21[/tex]
which is option c