Step-by-step explanation:

9y - 5x = 20
or, (9y - 5x) / 20 = 1
or, 9/20 y - 1/4 x = 1
compare with x/a + y/b = 1
you'll get
x intercept (a) = -4
y intercept (b) = 20/9
Unit walking rate in miles per hour = 5 2/3 / 2 2/3 = 17/3 / 8/3 = 17/3 x 3/8 = 17/8 = 2 1/8 miles per hour.
Unit walking rate in hours per mile = 1/ 17/8 = 8/17 hours per mile.
You have to add them all together and times that by 60%, when you get 13.8 that's the answer and to prove it, subtract 23-13.8 and you get 9.2 and that's 40%