= Solution
Using the stated curve assignments, read approximately $C_{t,S}=24$ and $C_{t,L}=26$ for Caco-2, and $C_{t,S}=24$ and $C_{t,L}=30$ for differentiated Caco-2. If both assays double product per cycle and have comparable threshold calibration,
$$
\frac{N_S}{N_L}=2^{C_{t,L}-C_{t,S}}.
$$
Therefore \b[TCF-short:TCF-long is approximately $4:1$ in Caco-2 and $64:1$ after differentiation]. The short:long ratio rises about sixteenfold; under the supplied legend, this pilot result does not support preferential expression of TCF-long after differentiation. These are approximate graph-based estimates, particularly because fractional-cycle readings can noticeably change a large ratio. Cross-assay molecule ratios require validated efficiencies and calibration standards; equal-looking plateaus do not establish either assumption.
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