Your question is a bit confusing but I am guessing you mean how far can she walk in 3 3/4 hours.
To obtain her speed in miles per hour, divide the 2 hours into 6 miles
6 miles ÷ 2 hours = 6 ÷ 2 = 3 miles per hour (3 MPH)
Now multiply 3 MPH with the time she walked to obtain the distance traveled.
3 MPH × 3 3/4 hours = 3 × 3 3/4 = 9 9/4 = 11 1/4 miles
