Write a full class definition for a class named GasTank, and containing the following members: A data member named amount of type double. A constructor that accepts no parameters. The constructor initializes the data member amount to 0. A function named addGas that accepts a parameter of type double. The value of the amount instance variable is increased by the value of the parameter. A function named useGas that accepts a parameter of type double. The value of the amount data member is decreased by the value of the parameter. A function named getGasLevel that accepts no parameters. getGasLevel returns the value of the amount data member.