First, Make 2 equations to show each company in which "x" equals the number of days:
Andy's Rental Car = 20 + (30x)
Buddy's Rental Car = 36 + (28x)
Set it up like this:
20 + (30x) = 36 + (28x)
Now, solve for x by simplifying both sides of the equation and then isolating the variable.
x = 8
8 Days