Answer:
526.5m
Step-by-step explanation:
Given parameters: 
Acceleration = 3m/s² 
Initial velocity = 21m/s 
Final velocity = 60m/s 
Unknown: 
Displacement = ? 
Solution: 
To solve this problem, we apply the right motion equation which is shown below; 
 V² = U² + 2aS 
 V is the final velocity 
 U is the initial velocity 
 a is the acceleration
 S is the displacement
 Insert the parameters and solve; 
 60² = 21² + 2(3)S 
 3600 = 441 + 6S
 3600 - 441 = 6S
 3159 = 6S
 S = 526.5m