10*(12+Х)=500;
120 + 10х = 500
10х = 500 - 120
10х = 380
х = 380 : 10
х = 38
проверка
10*(12+38)=500
10*50 = 500
500 = 500
5*10*у=250;
50у = 250
у = 250 : 50
у = 5
проверка
5*10*5=250;
50*5=250
250=250
(с-50)*3=600
с-50 = 600 : 3
с-50 = 200
с = 200 + 50
с = 250
проверка
(250-50)*3=600
200*3=600
600=600