Given: Isotope $"x"$ is used as a radictherapy source for treating cancer patiem tumors. The plot below gives the fraction of isotope $"x"$ remaining versus time in hours.

$2$a$.$ What is the half tife $T_1,2$ if isotope $-$X$"$ desermined using the plot. Stzle units: whxest sumple firtses tione in hours.