Answer:
The answer to your question is Kevin is 6 years old.
Explanation:
Process
1.- Assign a letter to Daniel and another letter to Kevin
Daniel = d
Kevin = k
2.- Write equation that help to solve this problem
  k = d + 3 equation l
 k = 4d equation ll four years ago
3.- Solve the system by substitution. Substitute equation ll in equation l
 4d = d + 3
-Solve for d
 4d - d = 3
 3d = 3
 d = 1
-Find k
 k = 1 + 3
 k = 4
4.- Calculate the age Kevin has now
Kevin's age = 4 + 2
 = 6