设甲的速度为$${a}$$千米/时，乙的速度为$${b}$$千米/时，  所以$$\left( {a}+{b} \right)\times 8=40$$ 从而推出$${a}+{b=}5$$．  $$\left( {a}-{b} \right)\times 5=5$$从而推出$${a}-{b=}1$$．  根据和差公式$${a=}\left( 5+1 \right)\div 2=3$$．  甲每小时行$$3$$千米．  速度和为$$40\div 8=5$$（千米$$/$$小时），  速度差为$$5\div 5=1$$（千米$$/$$小时），  甲速度为$$\left( 5+1 \right)\div 2=3$$（千米$$/$$小时）． 
$$A$$ and $$B$$ are $$40$$ kilometers apart. Two people, Alice and Bob, start from $$A$$ and $$B$$ at the same time and travel in opposite directions, meeting after $$8$$ hours. If two people leave $${A}$$ at the same time and go to $${B}$$, Alice is $$5$$ kilometers ahead of Bob after $$5$$ hours. Alice travels  kilometers per hour.  $$A$$，$$B$$两地相距$$40$$千米．甲、乙两人，同时分别由$$A$$，$$B$$两地出发，相向而行，$$8$$小时后相遇．如果两人同时由$${A}$$地出发前往$${B}$$地，$$5$$小时后甲在乙前方$$5$$千米处．则甲每小时行千米． 
[a] $$3$$ 
[b] $$4$$ 
[c] $$5$$ 
[d] $$6$$ 
[e] $$7$$ 