Amanda:  let  t  represent her time

                                  d = rt = 6t

Sarah:  t + 1  represents her time

                                d = 4(t + 1)

When Amanda and Sarah passe each other:

              6t + 4(t + 1)  =  34

              6t + 4t + 4  =  34

              10t + 4  =  3 4

              10t  =  30

                 t  =  3