Answer:
A
Step-by-step explanation:
b must always be greater than 0 since 12b-15 must always be greater than 21. You can simplify the ineqaulity to see things easier; 12b>36. Again, this ineqaulity can be simplified; b>3. A is the closest answer here, but there should be an open interval at 3 for A to be correct.
