Answer :
Given the expression:
[tex]\frac{ab}{2}[/tex]we have that when a=6ft and b=8ft, then:
[tex]\begin{gathered} a=6ft \\ b=8ft \\ \Rightarrow\frac{a\cdot b}{2}=\frac{(6ft)(8ft)}{2}=\frac{48ft^2}{2}=24ft^2 \end{gathered}[/tex]therefore, the result of the evaluated expression is 24ft^2