(HELP ASAP) Do these pairs of values (x and y) represent two quantities that are proportional?

You paid 28.00 for 8 gallons of gasoline. how much would you pay for 15 gallons of gasoline?

If the sales price of a dvd is $20 and the markup is 34%, what is the cost of the dvd?

Abaseball team drinks 10/4 gallons of water during a game. which mixed number represents the gallons of water consumed? a) 1 1/2 gallons b) 2 1/2 gallons c) 2 3/4 gallons d) 3 1/2 gallons