200×(х+71)=54000 900×(16-с)=5400 400×(х-12)=3600

200 * (х + 71) = 54 000 х + 71 = 54 000 : 200 х + 71 = 270 х = 270 - 71 х = 199 _____________ 200 * (199 + 71) = 54 000 900 * (16 - с) = 5400 16 - с = 5400 : 900 16 - с = 6 с = 16 - 6 с = 10 ___________ 900 * (16 - 10) = 5400 400 * ( х - 12) = 3600 х - 12 = 3600 : 400 х - 12 = 9 х = 9 + 12 х = 21 _________ 400 * (21 - 12) = 3600