300–x*5=210
(300–x)*5=210
(150–20):x=65
(x+4)*7=350
(300–18)*x=1410
5*x–600=900

х*5 = 300 - 210 = 90
х=90*5 = 18
300-х = 210:5= 42
х=300-42=258
130:х=65
х=130:65=2
х+4=350:7=50
х=50-4=46
282*х=1410
х=1410:282=5
5*х=600+900=1500
х=1500:5=300