Vindy paddles her kayak upstream at w kilometers per hour, and then returns downstream the same distance at n kilometers per hour. How many kilometers upstream did she travel if she spent a total of p hours for the round trip?	Choose the correct choice:
A) wnp  B) wn/p  C) (w + n)/p  D) wnp/(w + n)  E) pm/n- pn/m
let t1 and t2 be the time taken to row upstream and downstream respectively   now,   t1=distance/speed=d/w   similarly,   t2=d/n (as same distance has to be rowed)   also,   t1+t2=p   therefore,   p=(d/w)+(d/n)   =d(w+n)/wn   d=wmn/(w+n)=wnp/(w + n)
<result>D</result>
Vindy paddles her kayak upstream at w kilometers per hour, and then returns downstream the same distance at n kilometers per hour. How many kilometers upstream did she travel if she spent a total of p hours for the round trip?