Please answer the question in image.

(BD)^2 = (AB)^2 + (AD)^2
(BD)^2 = (4)^2 + (3)^2 = 25
BD = √25
      =  5
Consider △BCD,

Area of △BCD =1/2 ​× BC × CD
                        =1/2 × BD × CG
                       ⇒BD ∗ CG = BC ∗ CD    ............(i)

Area of rectangle BDFE = BD × FE = BD × CG = BC × CD     ( FE =CG ∵ FE=CG and eqn (i))
Area of rectangle BDFE = BC × CD = 3 × 4 = 12 cm^2