Answer
Please see the work below.
Work Step by Step
We know that the buoyant force is given as
$B=\rho_{air}Vg$
The weight of the Styrofoam is given as
$W=mg=\rho_{S}Vg$
Now we can find the percent error as
$\frac{B}{W}\times 100=\frac{\rho_{air}Vg}{\rho_SVg}\times 100=\frac{\rho_{air}}{\rho_S}\times 100=\frac{1.2}{160}\times 100=0.75\%$
