Planetary Reflectance vs Relative Spectral Response

I am confused between a Planetary Reflectance and the Relative Spectral Response (RSR). What I know/guess is that RSR is a response/function of an Instrument band's reflectance against a spectral range. Isn't that reflectance the Planetary Reflectance?

I am trying to solve this problem:

If the soil spectra was obtained at 10:20 am in January 5, 2005 at 14° 20’ N 121° 13’ E, compute for the spectral radiance of soil at a) sea level, b) extra-terrestrial level. On this day, the Landsat ETM+ satellite passed over the area. Neglecting atmospheric effects, what is the possible radiance detected by the sensor in the four bands?

I am given with:

1. Solar Irradiance values in a) Sea Level and b) Extra-Terrestrial Level which is also a response/function against a range of wavelength.
2. RSR for Landsat-7 ETM+
3. Spectral Signature of soil which is also a reflectance function/response against a spectral range.

Using the reference below, I need to compute for the Spectral Radiance . I can use the RSR and and Solar Irradiance to compute for Mean Solar Exoatmospheric Irradiance, Esunλ. The Earth-Sun distance d has a Julian Calendar table while the Solar zenith angle θs can be computed using the given date and time in the question. Where can I get the Planetary Reflectance to solve this problem? Is it the reflectance for a wavelength in the RSR?

Reference: