Answer: His rate is $ 55 per hour plus $278 material charge.
Explanation:
According to the question,
Carpenter's charge free from material charge for 15 hours = $825
Thus, Her charge free from material charge for 1 hours =

=

Thus, She charged $55 for 1 hours plus $278 material.
Therefore, her rate per hour = $55 per hour plus $248 material charge.