Car speed = 70km/h

Car            X  |——————————|———————>| Y

                     1300                        1600                         1800

                        <——?——-><— 10—–>

Lorry        X  |<—————|————-|———————-| Y                                                                                                                ?                  1600                               1300    

                                       Lorry average speed = ?

(a) Distance travelled by car from X to Y = 70 x 5 = 350

      Distance travelled by car up to 1600 = 70 x 3 = 210

      Remaining distance lorry needs to travel to X = 210 – 10 = 200

      Distance travelled by lorry  = 350-200 = 150

       Time taken for that distance = 3

       Therefore, average speed of lorry = 150/3 = 50km/h

(b)  Time taken to reach X for lorry = 200/50 = 4

Hence Lorry will reach X at 1600+ 4h = 2000

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