Answer:
The difference in force = 67500N
Step-by-step explanation:
The mass, m = 75 kg
The change in velocity, △v = 30 m/s
The force is calculated using the formula:

For the crash test without a seatbelt:
Time elapsed, △t = 0.03 seconds
Substitute m = 75, △v = 30, and △t = 0.03 into the formula above

For the crash test with a seatbelt:
Time elapsed, △t = 0.3 seconds
Substitute m = 75, △v = 30, and △t = 0.3 into the formula given

The difference in force = 75000 - 7500
The difference in force = 67500N