The Sun will become a red giant 2000 times more luminous than today when it fuses hydrogen. Assuming 40% of the Sun's original hydrogen is fused during this phase and 74% of the Sun's mass is originally hydrogen, the Sun will be a red giant for a calculated period of time.

1. When the Sun becomes a red giant, its luminosity will be
about 2000 times greater than it is today. Calculate how long our Sun
will be a red giant, assuming: that this luminosity is caused only by the
fusing of hydrogen, that only 40% of the Sun's original supply of
Hydrogen is fused during the red giant phase, and that 74% of the
original mass of the star is in the form of Hydrogen.