Answer:
you multiple the y-intercept and then multiply the x-intercept and then find the slope.
Step-by-step explanation:
I don't know the answer, but I suggest downloading the app: PhotoMath. It scans a math problem and shows you how to complete the problem. I hope this helped~!
Because if you multiply 2 different irrational numbers (like the following)

You will get an irrational answer.
BUT
if you multiply the same square root (which are both irrational, you get a rational number)
a. (2175 mi)/(18 mi/day) = 120.83... day ≈ 121 days
b. 120.83.../4 = 30.2083...
Joelle will hike 30 full days and one partial day.