If 30 marks is 40%,what is full marks

Which expression is equivalent to? assume x > 0 and y > 0.

Janie has $3. she earns $1.20 for each chore she does and can do fractions of chores. she wants to earn enough money to buy a cd for $13.50. write an inequality to determine the number of chores, c, janie could do to have enough money to buy the cd.

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?