[tex] \huge\colorbox{black}{ \color{white}{ANSWER}}[/tex]
we know,
[tex]\mathfrak{\hookrightarrow { area = \dfrac{1}{2} \times (a + b) \times h }}[/tex]
where,
So,
[tex] \hookrightarrow \mathcal{28 = \dfrac{1}{2} \times (5 + 2) \times h}[/tex]
[tex]\hookrightarrow \mathcal{28 \times 2 = 7 \times h}[/tex]
[tex]\hookrightarrow \mathcal{ \dfrac{56}{7} = h}[/tex]
[tex]\hookrightarrow \mathcal{h = 8}[/tex]
so, missing lenght = 8 cm