The answer for this question would be B. f(x) = 7x + 6
For questions like this, you would plug in the first number on the left side of the chart into this equation and use that number instead of x.
So it would be:
f(x) = 7(1) + 6
That equals 13 because f(x) = 13
That number matches the first number on the right side of the chart and continues to work with each set of numbers, going down the chart. I hope this helps!