There are $$15$$ chairs and $$20$$ cups. So the ratio of chairs to cups is $$15:20$$. The simplest form is $$3:4$$. 
In a dining room, there are $$15$$ chairs, $$5$$ tables, and $$20$$ cups. What is the ratio of chairs to cups in the simplest form? 
(a) $$1:4$$ 
(b) $$15:20$$ 
(c) $$4:3$$ 
(d) $$3:4$$ 