The area of a trapezoid is given by:
[tex]\begin{gathered} A=\frac{a+b}{2}\cdot h \\ \text{Where:} \\ a=\text{ Long base}=12 \\ b=\text{ Short base}=8 \\ h=\text{height} \\ A=\text{Area}=60 \end{gathered}[/tex]Replacing the data into the equation:
[tex]\begin{gathered} 60=\frac{12+8}{2}\cdot h \\ 60=\frac{20}{2}\cdot h \\ 60=10\cdot h \\ \text{Solving for h:} \\ h=\frac{60}{10} \\ h=6m \end{gathered}[/tex]