1)a+4200=9000
a=9000-4200
a=4800
4800+4200=9000
2)7660-a=4782
a=7660-4782
a=2878
7660-2878=4782
3)x×100=88900
x=88900÷100
x=889
889×100=88900
4)b-3705=5000
b=5000+3705
b=8705
8705-3705=5000
5)497+c=5300
c=5300-497
c=4803
497+4803=5300
6)x÷100=7560
x=7560×100
x=756000
756000÷100=7560
7)c-98=1300
c=1300+98
c=1398
1398-98=1300
8)147+b=5007
b=5007-147
b=4860
147+4860=5007
9)90000÷x=3
x=90000×3
x=270000
270000÷90000=3