1) the superclass calculator contains:
a) a (protected) double instance variable, accumulator, that contains the current value of the calculator.
b) write a subclass
2) calculator with memory, that contains:
a) a double instance variable, memory, initialized to 0
b) a method, save, that assigns the value of accumulator to memory
c) a method, recall, that assigns the value of memory to accumulator
d) a method, clearmemory, that assigns zero to memory
e) a method, getmemory, that returns the value stored in memory