How much change do i get back if i buy a candy bar for 0.78 from a1.00 bill

How many different ways can you make change for $.50 using only nickels, dimes, and quarters?

Mr switzer needs to buy new 1-foot tiles to cover his bathroom floor. the floor is 12 feet long and 8 feet wide. each square foot of tile will cost $1.79. in dollars what will be the total cost of the tiles he needs to buy.

How do i do this activity, is appreciated