Y = x + 2 is closest to what I believe is the solution.
If the club begins with 2 members, then +2  MUST appear in the formula.
If the club adds 2 members every week, then the total number of members would be
f(x) = y = 2 + 2(x-1), where x is the number of weeks.
Test this:  If x = 1, then y = 2+2(1-1) = 2 + 0  = 2.  This is correct.  The club began with 2 members in week 1
        
                    
             
        
        
        
4x + 17 = 23
23-17=6
4x=6
6/4=1.5
 X=1.5
Hope this helps
        
                    
             
        
        
        
Answer:
ok
Step-by-step explanation:
 
        
                    
             
        
        
        
Fun fact
if f(a)=b then f⁻¹(b)=a
so
if f⁻¹(b)=a then f(a)=b
 
so we find f(x)=27 and the solve for x
f(x)=3x=27
3x=27
divide both sides by 3
x=9
so if f(9)=27 then f⁻¹(27)=9
problem solved
answer is 9