Answer:
I'm sorry I don't know the equation, but she walks 3 mph.
Step-by-step explanation:
We know that the answer is asking for speed, which needs both distance and time, so we also need both. Which is where the 9 mph is used. 9 mph means its a difference. b means biking mph, w means walking mph, sooo ----->>> b=w+9, and the difference in the 1st equation is 36, which means the first equation is 4 times larger than the b=w+9, so she walked 48 miles, as well as walked 12 miles in 4 hours. Divide then distances by 4, and you get 12 miles and 3 miles in one hour. Or 12 mph & 3 mph, which fits into 12=3+9. So she walks 3 miles per hour.
