One third of a number less than 9 equal to 7

Can someone me with this problem . show your work .

The price of a dozen eggs was $1.63. suppose the price increases m dollars per dozen and then the price decreases $0.12 per dozen. which expression represents the current price of eggs after the two price changes?

The sum of the speeds of two trains is 720.2 mph. if the speed of the first train is 7.8 mph faster than the second train, find the speeds of each.