Bài giải:

S.DFC = $\frac{1}{3}$x S.DBC = $\frac{1}{6}$ x S.ABCD = $\frac{1}{6}$ x 144 = 24 (cm²) S.ADE = $\frac{2}{3}$x S.ABD = $\frac{1}{3}$x S.ABCD = $\frac{1}{3}$ x 144 = 48 (cm²)

S.BEF = $\frac{1}{3}$x S.FAB = $\frac{2}{9}$x S.ABC = $\frac{1}{9}$ x S.ABCD = $\frac{1}{9}$ x 144 = 16 (cm²)

Vậy S.DEF = S.ABCD – S.DFC – S.ADE – S.BEF

                    = 144 – 24 – 48 – 16 = 56 (cm²)

                                        Đáp số: 56cm²