You shouldn't have any trouble with this one, if you remember the formula for an object's momentum:
Momentum = (mass) x (velocity) .
For the truck: m= 2,120 kg, v= 26 m/s east.
Truck momentum = (2,120 kg) x (26 m/s east)
For the car: m= 1,350 kg
Car momentum = (1,350 kg) x (speed m/s east)
They're supposed to be EQUAL !
So Truck momentum = Car momentum .
(2,120 x 26 east) = (1,350 x speed east)
Surely you can take this and figure out what 'speed' is.
