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What is the difference between regular convex and concave polygons

10 ! a train starts from grand city and travels toward belleville 388 miles away. at the same time, a train starts from belleville and runs at the rate of 47 miles per hour toward grand city. they pass each other 4 hours later. find the rate of the train from grand city.

The difference of three and the reciprocal of a number is equal to the quotient of 20 and the number. find the number.