For each proposition below, either i. use a case-based proof to demonstrate that the proposition holds or ii. Use a counterexample to demonstrate the proposition does not hold. (a) Assume x is an integer that is not divisible by 4, and y is an integer that is divisible by 4. Then the sum of x and y cannot be divisible by 4. (b) Assume x is an integer that is not divisible by 4, and y is an integer that is divisible by 2. Then the sum of x and y cannot be divisible by 4.