How can I make a variation formula out of this table??

I'm going to add a few missing terms (that fit the pattern that you gave):

x  =  1      2      3     4     5     6     7

y  =  7    11    15    19    23   27    31

 

Notice that as each x-term increases by 1, the corresponding y-term increases by 4.

This means that this is a linear equation with slope = 4.

y  =  mx + b                   (with m = 4)

y  =  4x + b

Now, substitute any (x,y) pair into this equation.  I'm going to use (5,23), but I could have used any pair.

23  =  4(5) + b

23  =  20 + b

3  =  b

 

This means that a possible equation is:  y  =  4x + 3.