$$1\textasciitilde\text{kg}$$ of strawberries costs $$2a+b$$,  so $$3\textasciitilde\text{kg}$$ of strawberries costs $$3\times (2a+b)=6a+3b$$.  So, the answer is C. 
In a fruit market, $$1\textasciitilde\text{kg}$$ of apples is priced at $$\textbackslash$a$$. $$1\textasciitilde\text{kg}$$ of strawberries costs $$\textbackslash$b$$ more than $$2$$ times $$a$$. How much will $$3\textasciitilde\text{kg}$$ of strawberries cost? 

a. $$3a+6b$$ 
b. $$2a+b$$ 
c. $$6a+3b$$ 
d. $$6a+b$$ 