It is given that,  $△ABC\cong △FDE and AB=5cm,\angle B=40°and \angle A=80°$. Then which of the following is true? 

Given, $△ABC\cong △FDE$ and $AB=5cm,\angle B=40°$and $\angle A=80°$

Using CPCT rule,

$DF=5cm \because AB=5cm$

Again using CPCT rule, $\angle E=\angle C$

$\therefore$ $\angle E=\angle C=180°$ $-$ ($\angle A+\angle B$) ,using angle sum property

$\angle E=180°$ $-$($80°+40°$)

$\angle E=180°-120°$

$\angle E=60°$