A multiple of $$3$$ and $$7$$ also a multiple of $$21$$  $$21\times3=63$$  $$21\times4=even$$  $$21\times5=105$$, exceed  Thus, only $$63$$ 
An unknown number is an odd number greater than $$50$$ but less than $$100$$. The number is a multiple of $$3$$ and $$7$$. What is the value of the unknown number? 
Options:
a. $$63$$ 
b. $$77$$ 
c. $$84$$ 
d. $$91$$ 
e. None of the above 