Please help me with this question

Answer:
D. The truck and trailer will experience a net force of 40 newtons backward
Explanation:
Taking the greatest force (trailer), and subtracting it by the smaller force (truck), we can find how many newtons the greater force is applying to pull the whole system:
2,790 - 2,750 = 40 N
Since we know that the trailer is the greater force, the truck & trailer are being pulled backwards by 40 Newtons