Okay, So An Equation To Write Is:
T = Time
S = Money Saved
R = Money Made Per Dog
C = Cost
T = (C - S)/R
Solve:
T = (108 - 30)/8
Simplify
108-30 = 78
T = 78/8
78/8 = 9.75.
T = 9.75
Now, You Can't Walk 0.75 Of A Dog, So Round It.
T = 10
So, You Need To Walk At Least 10 Dogs.