The area of an equilateral triangle having sides 20m, is:-  

100\(\sqrt {3}\)

Area of an equilateral triangle = \(\frac{\sqrt {3}}{4} × a^2\)

                                            = \(\frac{\sqrt {3}}{4} × 20^2\)

                                            = \(\frac{\sqrt {3}}{4} × 400\)

                                            = \(100 \sqrt {3}\)