If the car has a horizontal velocity of 26m/s and lands 80m from the base of the cliff then to work out time taken is simply distance/speed, 80/26=3.08s
From here you can substitute the values of u (0m/s), a (9.81m/s^2) and t (3.08s) into the equation s = ut + 1/2at^2 to find the height of the cliff