help me solve this

examp. 12:00 start Ali                              Bakar:  4km ->1h

             12:30 start Bakar                         6km->xh    <=> x=3/2h <=> x=90 min +12:30= 2:00 

                                                                 arrived at the same time so Ali arrived at 2 so he do:

                                                                  6km->2h

                                                                  ykm->1h <=>y=3km so 3km/h is the Ali's average speed!!!

 I hope you understand!!!

Average speed = Distance / Time

4= 6/ T, so T =6/4 =1.5 hours - that took Bakar to cover the 6 Km.

Ali's average speed = 6/ (1.5 + .5) =6 / 2 =3 Km/h - Ali's average speed.

Bakar's Distance divided by his rate  = his total time   =  6km / [ 4km/h ]  =  3/2 hr

And Ali's Distance  divided by his unknown rate , R,  rate  = his total time  = 6km / [ R km / h ]

And Bakar's time  plus 1/2 hr   =   Ali's time .......so

(3 / 2)   + (1/ 2)  = 6 / R   simplify

[ 6 + 2] / 4=   6 / R

[ 8 / 4]   = 6 / R

2 = 6 / R     and we can write

1/2 =  R / 6    multiply both sides by 6

3  = R      and Ali's rate  = 3 km / hr