Let, coordinate of point A' is (x,y).
Since, A' is the symmetric point A(3, 2) with respect to the line 2x + y - 12 = 0.
So, slope of line containing A and A' will be perpendicular to the line 2x + y - 12 = 0 and also their center lies in the line too.
Now, their center is given by :

Also, product of slope will be -1 .( Since, they are parallel )

x = 2y - 1
So, 
Also, C satisfy given line :

Also,

Therefore, the symmetric points is
.
20,000 x 25 = 500,000
500,000 divided by 100 = 5,000 members are lost.
Members left = 15,000
Members added = 10,000
Members every year = Members left + Members added
= 15,000 + 10,000
= 25,000
1060.5263157 etc your teacher prob tells you to round