Answer
$70\;lb$.
Work Step by Step
A pound of sea water $\rightarrow 35$ parts per thousand.
$1$ pound of sea water $ \rightarrow \frac{35}{1000}\;lb$
Use $1$ tons of seawater $=2000$ pounds of seawater.
Therefore,
$1$ tons of sea water $=2000\times \frac{35}{1000}\;lb$
Simplify.
$1$ tons of sea water $=70\;lb$.
