let x = cost for a night. y = cost to rent car for a day.
Connor = 3 nights and 4 days = 3x + 4y = 675
Jillian = 4 nights and 5 days = 4x + 5y = 875
3x + 4y = 675 Multiply by 5
4x + 5y = 875 Multiply by 4
53x + 54y = 5675 15x + 20y = 3375
44x + 45y = 4875 16x + 20y = 3500
15x + 20y = 3375
-
16x + 20y = 3500
________________
-x + 0 = -125
x = 125
The cost per night is x, = $125