∵△ABD和△ACD等底同高面积相等,∴ S△ABD=1/2S△ABC
∵△ABE是△ABD底长的1/3,高相同, ∴ S△ ABE=1/3 S△ABD=1/6 S△ABC
∵△AEF是△ABE底长的3/4,高相同, ∴ S△AEF=3/4 S△ABE=1/8 S△ABC=1/8*180=22.5cm²