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Two motor-cyclists John and Kevin were $800 \text{km}$ apart and travelling towards each other at a constant speed. They started at the same time, meeting after $8$ hours. If Kevin started $1\dfrac{1}{2}$ hours later than John, they would be $70 \text{km}$ apart $8$ hours after John started. At what speed was John travelling in $\text{km/h}$? 
1. $$50$$ 
2. $$51 \frac{2}{3}$$ 
3. $$52 \frac{1}{2}$$ 
4. $$53 \frac{1}{3}$$ 
5. None of the above 