900-х:5=800
х:5=900-800
х:5=100
х=5*100
х=500
900-500:5=800
3•x-80:4=25
3х - 20 = 25
3x = 25+20
3x = 45
х=45:3
х=15
900-х:5=800
х:5=900-800
х:5=100
х=5*100
х=500
900-500:5=800
3•x-80:4=25
3х - 20 = 25
3x = 25+20
3x = 45
х=45:3
х=15