Answer:
130 degrees
Explanation:
We already know that CD = 100.
We also know that all 3 arcs in this circumscribed circle have to equal 360.
So, let's write an equation and solve for BC:
BC+CD+BD=360
BC=BD
we know this because side lengths BC and BD are congruent
(BC+BD)+100=360
we can combine like terms and substitute in our known value of CD
BC+BD=260
subtract 100 from both sides
BC+BC=260
substitute in BC=BD
2BC=260
combine like terms
BC=130
divide both sides by 2 to get BC
This means that option C (130 degrees) is correct. Hope this helps! :)