I run $$2\text{km}$$ in $$15$$ minutes, or $$8\text{km}$$ in $$1$$ hour. In $$2$$ hours, I will run $$16\text{km}$$ and my sister will run $$20\text{km}$$. She will run $$4\text{km}$$ farther than I will. 
My sister runs $$10\text{km}$$ per hour, and I run $$2\text{km}$$ in $$15$$ minutes. If we both run for $$2$$ hours, my sister will run$$\text{km}$$ farther than I will. 
[1] $$2$$ 
[2] $$4$$ 
[3] $$6$$ 
[4] $$8$$ 