A fair sells a``combo" ticket for ＄$$30$$ entry and a ``per ride" ticket for ＄$$12.50$$ to enter plus ＄$$5$$ per ride. A``per ride" ticket costs ＄$$12.50+$$ ＄$$15 =$$＄$$27.50$$ for $$3$$ rides and ＄$$12.50 +$$ ＄$$20 = $$＄$$32.50$$ for $$4$$ rides. 
A "combo"~ticket to enter the fair and ride unlimited rides is ＄$$30$$. A``per ride" ticket costs ＄$$12.50$$ to enter and ＄$$5$$ per ride. For a"combo''ticket to cost less than a "per ride" ticket, a person must go on at least  rides. 

* $$3$$ 
* $$4$$ 
* $$6$$ 
* $$7$$ 