Two Stages, One Target Score

A sensor feeds a raw reading $x$, in millivolts, into a two-stage pipeline. Stage 1 rescales the reading; stage 2 turns the rescaled number into a score.

Stage 1 runs first, and its output is the only thing stage 2 ever sees. So the pipeline as a whole is the composition

$S(x) = f\big(g(x)\big)$

If you sketch the graph of $y = S(x)$, the curve crosses the horizontal line $y = 6$ at exactly two points.

Report the $x$-coordinate of the right-hand crossing — that is, the larger of the two raw readings that make the pipeline output a score of $6$.

Give your answer in millivolts, rounded to two decimal places if needed.