1) 18*x=90 x = 90:18 = 5 18*5=90
2) 720:x=4 x = 720:4= 180 720:180 =4
3) 350:x=5*10 x = 350:50 = 7 350:7 = 50 = 5*10
4) x:30=60*5 x = 60*5*30 = 9000 9000:30 = 300 = 60*5
5) x*100=4500 x = 4500:100 = 45 45*100 = 4500
6) x:10=45000 x = 45000*10 = 450000 450000:10 = 45000