Check the picture below.
[tex]\bf \textit{area of a trapezoid}\\\\ A=\cfrac{h(a+b)}{2}~~ \begin{cases} a,b=\stackrel{bases}{parallel~sides}\\ h=height \end{cases} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{left-side trapezoid}}{ \begin{cases} a=2\\ b=5\\ h=3 \end{cases}}\implies A=\cfrac{3(2+5)}{2}\implies A=\cfrac{21}{2}\implies A=10\frac{1}{2} \\\\\\ \stackrel{\textit{right-side trapezoid}}{ \begin{cases} a=1\\ b=4\\ h=3 \end{cases}}\implies A=\cfrac{3(1+4)}{2}\implies A=\cfrac{15}{2}\implies A=7\frac{1}{2}[/tex]
