momentum = mass * velocity
For the car:
momentum = 800 kg * 26 m/s = 20,800 kg-m/s
For the truck:
momentum = 12,500 kg * 19 m/s = 23,750 kg-m/s
How much does the car have more or less?
momentum (car)/momentum (truck) = 20,800/23,750 = 0.876 = 0.876 times