Hi carlos.lara.7,

This question is ultimately about translating words into 'math.' We're told that plan M allows users a certain number of minutes of phone calls. Any extra minutes beyond the plan 'limit' are charged at $0.50 for each additional minute. We're asked for the number of minutes allowed by plan M.

1) The cost of exceeding the limit by 50 percent is $75.

From the prompt, we know the price of each additional minute. Fact 1 tells us that $75 in extra fees will be added on IF the total number of minutes increase by 50%. That extra $75, at $0.50/minute, equals 150 minutes of extra calls. We're told that this is equal to a 50% increase over the plan, so....

150 minutes = (50%)(plan M)
300 minutes = plan M

We now know the answer to the question.
Fact 1 is SUFFICIENT

2) A client who exceeds plan M by $75 uses 3/4 as much telephone time as a client who exceeds plan M by $150.

From this Fact, and the information in the prompt, we know a few things:
$75 extra = 150 extra minutes
$150 extra = 300 extra minutes

(plan M + 150) = (3/4)(plan M + 300)
(plan M + 150) = (3/4)(plan M) + 225

(1/4)(plan M) = 225 - 150
(1/4)(plan M) = 75
plan M = 300 minutes

We now know the answer to the question.
Fact 2 is SUFFICIENT

Final Answer: D

GMAT assassins aren't born, they're made,
Rich