Answer:
4 hours
Explanation:
First we find the distance between the library and Molly's house.
The line segment from Molly's house to Raven's house, 3 miles, and the line segment from Raven's house to the library, 4 miles, form the legs of a right triangle. Using the Pythagorean theorem,
a²+b²=c²,
3²+4²=c²
9+16=c²
25=c²
Take the square root of each side:
√(25) = √(c²)
5 = c
This makes the total number of miles Molly walks
3+4+5 = 12 miles.
Since she travels 3 miles per hour, she travels 12/3 = 4 hours.