Answer: C. Substitution Property of Equality
Explanation:
The substitution property of equality says that if a=b, then 'b' can be substituted in the place of 'a' or 'a' can be substituted in the place of 'b'.
For example : If a= 7 and b=a-2
Then we substitute a=7 , we get b=7-2=5
Similarly, we are given that If x=3 and y=x+5, then y=8
Here the value of x is substituted as 3, then y=3+5=8
Hence, the property of equality that justifies given statement : Substitution Property of Equality