In an experiment on the transport of nutrients in the root structure of a plant, two radioactive nuclides $\mathrm{X}$ and $\mathrm{Y}$ are used. Initially, 2.50 times more nuclei of type $\mathrm{X}$ and $\mathrm{Y}$ present than of type Y Precisely three days later, there are 4.20 times more nuclei of type $\mathrm{X}$ than of type $\mathrm{Y}$ . Isotope $\mathrm{Y}$ has a half-life of $1.60 \mathrm{d} .$ What is the half-life of isotope $\mathrm{X}$ ?