<PRE><B>Question 200410</B>
Let  K  =  velocity  of  Keiko,,,,,,,Let J = velocity  of  Javier  ( km/hr),,,,Let  t = time  (hrs)
.
K= J + 4
.
J=30 /t,,,,,,,K=42/t
.
42/t = 30/t +4,,,,,,,,,,  (substitute  into  (1)  )
.
42 = 30 +4t,,,,,,,,,,,,,,,( multiply thru  by  t)
.
12 = 4t
.
t = 3 hrs
.
J=30 /3 =10  km / hr,,,,,,,,,K=42 /3 =14  km/hr,,,,,ANSWER
.
checking  in  (1)  14 = 10 +4,,,,,ok</PRE>