0.36×72＋45×0.18＋45=0.36×72＋45×(0.18＋1)=0.36×72＋45×1.18=0.36×72＋(45x3)×1.18/3=0.36x72+0.36X135=0.36X(72+135)=0.36X208=0.36X200+0.36X8=72+2.88=74.88