Deliver the pastries

Kevin leaves his bakery at 6.50 am to deliver some pastries to a hotel. If he drives at a constant speed of 80km/h, He will reach the hotel on time. If he drives at a constant speed of 64km/h, he will be 10mins late. At what time is Kevin supposed to deliver the pastries to the hotel?

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distance = rate x time

at 80 km/hr
d = 80t

at 64 km/hr
d = 64(t + 1/6)   {time plus 10 minutes or 1/6 of an hour}

80t = 64(t + 1/6)   {the distances are equal}
80t = 64t + 32/3   {used distributive property}
16t = 32/3   {subtracted 64t from each side}
t = 2/3   {divided each side by 16}
2/3 of an hour is 40 minutes

Add 40 minutes onto 6:50 am

He is supposed to arrive at 7:30 

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