Use the distributive property of multiplication.
25(-5x/2)=-62.5x, and 25(1/2)=12.5.
Add these together:  -62.5x + 12.5 (answer)
        
             
        
        
        
If you didn't change the slope of the line, but you moved it 
down 6 units on the graph, then its y-intercept would become 
6 less.  The equation of the new line would be ...
                  y = 1/3 x - 16 .
        
             
        
        
        
Use the formula
a_n = a_1•r^(n-1)
a_23 = 25•(1.8)^(23 - 1)
Can you finish?