A Cepheid star and non-Cepheid star both belong to the same distant galaxy. Explain, stating the quantities that need to be measured, how the luminosity of the non-Cepheid star may be determined.

measure period and average apparent brightness/magnitude of the Cepheid to determine its distance;
measuring the apparent brightness of the star gives the luminosity (since distance is now known) from L=4πd²b;

or

measure period of Cepheid to determine its (average) luminosity;
compare the apparent brightness of the star and Cepheid to find L using L∝b;