A manager is seeking to maximize profits based on two products, x and y, which yield $10 and $15, respectively. There are 20 hours each day available and each unit of x requires 4 hours while each unit of y requires 3. According to the optimal solution, how many hours are left unused? Assume the optimal solution can be non-integer.

a.

0

b.

1

c.

2

d.

3