There are $$3$$ groups of $$5$$ buns in $$15$$ buns: $$15\div 5=3$$, so $$5$$ buns cost $$6\div 3=$$＄$$2$$.  In total, Tom bought $$15 + 5 = 20$$ buns, which is $$4$$ groups of $$5$$ buns. So, Tom paid $$4\times 2 =$$＄$$8$$. 
Adam paid ＄$$6$$ for $$15$$ buns. How many dollars did Tom pay for the same kind of buns if he bought $$5$$ more of them? (2008 Math Kangaroo Problem, Level 1-2, Question \#13) 
Options:
1. $$7$$ 
2. $$8$$ 
3. $$9$$ 
4. $$10$$ 