Answer
$x=\frac{3.20}{0.22}\approx 14.55$
Work Step by Step
$\displaystyle \frac{1.73x}{2.12+x}=1.51$
We cross multiply:
$1.73x=1.51(2.12+x)$
And distribute:
$1.73x=3.20+1.51x$
And combine $x$ terms:
$0.22x=3.20$
And solve for $x$:
$x=\frac{3.20}{0.22}\approx 14.55$