Answer:
Option C is correct.

Step-by-step explanation:
Given the expression: 
Using properties of summation:
Using properties of summation in the given expression we have;
= 
=
Therefore, the following given expression uses the properties of summation to represents is, 
Answer:
21
Step-by-step explanation:
what dou you need?????????
Answer:
25.5 and 37.5
Step-by-step explanation:
x+y=63
x-y = 12 then x = 12 + y sub this into the first equation
(12+y) + y = 63
12 + 2y = 63
2y = 51
y = 25.5 then x = 37.5