Approximately what mass of ⁹0Sr (t₁/₂ = 28.8 yr) has the same activity as 1 g of ⁶0Co (t₁/₂ = 5.26 yr)? (Hint: Refer to isotopic masses for ⁹0Sr and ⁶0Co.)

a) 1.32 g
b) 2.30 g
c) 3.64 g
d) 4.91 g