1)(90+ x)×4=660
x=660÷4-90
x=165-90
x=75
(90+75)×4=660
660=660
2)(90+120)× x=1260
x=(90+120)÷1260
x=210÷1260
x=6
(90+75)×6=1260
1260=1260
1)(90+ x)×4=660
x=660÷4-90
x=165-90
x=75
(90+75)×4=660
660=660
2)(90+120)× x=1260
x=(90+120)÷1260
x=210÷1260
x=6
(90+75)×6=1260
1260=1260