Generally, you shouldn't post more than two problems in a thread, as per Rule 8.
For # 1, I would just write out a truth table, and check to see which rows, if any, satisfy all the conditions.
For # 2, can you post your work so far?
For # 3, I would recommend working in units of cents, not dollars. Then impose the condition that x, y, and z must all be integers. That might narrow down the solution space a bit for you.