You probably would have received help faster had you posted only one problem at a time. Try that next time you want help.
Regarding your first question: "How many different ways can you obtain a total of 50 cents with 7 or fewer coins?" I'd suggest you write out as many combinations of 7 or fewer coins as you can that add up to 50 cents.
Examples:
Five dimes (5 coins) add up to 50 cents.
Three dimes and four nickels (7 coins) add up to 50 cents.
Keep going until you've run out of possibilities.