Answer
$m_{t}=84.08lbm$
$x=0.0501$
Work Step by Step
$V_{f}=0.2*5ft^3=1ft^3$
$V_{g}=0.8*5ft^3=4ft^3$
From table A-12E:
$\upsilon_{f}=0.01252\frac{ft^3}{lbm}$
$\upsilon_{g}=0.94909\frac{ft^3}{lbm}$
Then:
$m_{f}=\frac{V_{f}}{\upsilon_{f}}=\frac{1ft^3}{0.01252\frac{ft^3}{lbm}}=79.87lbm$
$m_{g}=\frac{V_{g}}{\upsilon_{g}}=\frac{4ft^3}{0.94909\frac{ft^3}{lbm}}=4.21lbm$
$m_{t}=m_{f}+m_{g}=79.87lbm+4.21lbm=84.08lbm$
$x=\frac{m_{g}}{m_{t}}=\frac{4.21lbm}{84.08lbm}=0.0501$
