What is the primary function of an operator in the regulation of transcription in bacteria?

What does the number 18.9984 represent in the image?

Cells a and b are the same size and shape, but cell a is metabolically quiet and cell b is actively consuming oxygen. oxygen will diffuse more quickly into cell because . b the oxygen molecules inside cell b have a higher kinetic energy b. a its membrane transport proteins will not be saturated c. a the diffusion gradient there is shallowerd. b the diffusion gradient there is steeper

What does the splanchnic nerve innervate?