At his college, Jason can take a maximum of 21 hours each semester between elective classes and core classes. Each elective class costs $225 per semester hour and each core class costs $275 per semester hour. If he cannot spend more than $6,000 each semester on classes, which system of inequalities below can be used to determine the number of elective classes, e, and the number of core classes, c, he can take each semester?
A.
e + c < 21
$225e + $275c > $6,000

B.
e + c < 21
$225e + $275c < $6,000

C.
e + c > 21
$225e + $275c > $6,000

D.
e + c < 21