Find the diameter of a circle whose area is equal to the sum of areas of 2 circles of radii 24cm and 7cm​

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.