Let x be the first number each pair and y is the second of each
As you see 1x is 3y
And. 2x is 3*3y= 9y
3x = 3*3*3y= 27y
Last 4x =3*3*3*3y= 81y
So y = 3^x
Each term is equal the preceding term plus 3. Therefore the next term is 13 and the difference is +3.
D, it’s a function because the Y and X values have its own numbers , and vertical are functions . Horizontal is not a function