Mass of Radioactive Substance After Half-Lives

Consider a spherical radioactive substance with a certain half-life. When initialized, the substance contains 80 grams. After one half-life, the amount of the substance would be reduced to 40 grams. This decay process follows an exponential decay model, which can be described by the equation: N(t) = N_0 imes (1/2)^{(t/T_{1/2})}, where N_0 is the initial quantity, N(t) is the quantity remaining after time t, and T_{1/2} is the half-life of the substance. What would be the mass of the substance after three half-lives?