We can use rule of three to answer that.
1 cubit --- 2.54 smoots
68.87 cubits --- x
[tex]\begin{gathered} \frac{1}{68.87}=\frac{2.54}{x} \\ 1\cdot x=2.54\cdot68.87 \\ x=174.9298\approx174.93 \end{gathered}[/tex]So, 68.87 cubits is approximately 174.93 smoots.