Answer: The reasons would be Given , Combine like terms , Subtraction Property of Equality.
Step-by-step explanation:
Since we have given that 

We have given some steps :
3+4x-3x=4  ( Given )
3+x=4  ( Combine like terms )
3-3 + x =4-3
x=1  (Subtraction Property of Equality )
Hence, the reasons would be 
Given , Combine like terms , Subtraction Property of Equality.