Question 344623
x     y
1     20
2     16
3     12
4     8
  
at each step +1 for x, we notice a step -4 for y, hence we could write : 
  
y(x)=20-4*(x-1)
  
for x=1, we have y=20-0=20
x=2 : y=20-4=16
x=3 : y=20-8=12
x=4 : y=20-4*3=20-12=8