Answer:
The coordinates of point R are (6 , 3)
Step-by-step explanation:
* Lets revise the rule of the mid-point
- The mid point (x , y)of a line whose end points are 
and
is 
∵ M is the mid point of line RS
∵ The coordinates of point M are (7 , 5)
∴ x = 7 and y = 5
∵ The coordinates of point R are 
∵ The coordinates of point S are (8 , 7)
∴
= (8 , 7)
∴
and
- By using the rule above
∵ 
∵ 
- Multiply both sides by 2
∴ 
- Subtract both sides by 8
∴ 
∴ the x-coordinate of point R is 6
∵ 
∵ 
- Multiply both sides by 2
∴ 
- Subtract both sides by 7
∴ 
∴ the y-coordinate of point R is 3
* The coordinates of point R are (6 , 3)