Step-by-step explanation:
The given figure is a trapezoid with area 20 sq cm and perpendicular height 4 cm.
[tex]aera \: of \: trapezoid \: \\ = \frac{1}{2} (sum \: of \: lengths \: of \: \parallel \: sides) \\\times height \\ \\ \therefore \: 20 =\frac{1}{2} (6 + a) \times 4\\ \\ \therefore \: 20 =(6 + a) \times 2\\ \\ \therefore \: 20 =12 + 2a \\ \\ \therefore \: 20 - 12 = 2a \\ \\ \therefore \: 8 = 2a \\ \\ \therefore \: a = \frac{8}{2} \\ \\ \: \: \: \: \: \: \huge \orange{ \boxed{\therefore \: a = 4}}[/tex]
