Question 1023781
For chess club:
y1 = 16 + 1*x where y1=total number of members after x months

For film club
y2 = 4 + 4*x where y2=total number of members after x months

y1 = y2 at

16 + x = 4 + 4x
3x = 12

x = 4


Therefore, after 4 months they the same number of members (equals 20 members, 16 + 1*4 or 4 + 4*4).