In a private closed economy, the equations I_{g} = 80 and S = -80 + 0.4Y describe the relationship between gross investment ( I_{g} ), saving ( S ), and gross domestic product (GDP) ( Y ). In equilibrium, where I_{g} equals S , what is the value of saving? Choose from the following options:
a) $40.
b) $120.
c) $60.
d) $80.