How long did it take Helen to drive from her house to her mother's house?

1. Her average speed was 72 mph.

2. If her average speed had been 8 miles per hour greater, it would have taken her 1 hour less.

The multiple choice answers are (it's a GMAT problem):

A. Statement 1 is enough, but not statement 2.

B. Statement 2 is enough, but not statement 1.

C. Both Statement 1 and 2 are needed to answer this question.

D. Either statement can be used to answer this question.

E. Neither statement can be used to answer this question.

I chose E, but this exam says that the answer is C. I just don't see how this can be solved without a total distance and a time.

Thanks in advance.