80000: y=4000-2000
80000:y=2000
y=80000:2000
y=40
12000x=800-30
12000x=770
x=77/1200
80000÷y=4000-2000
80000÷y=2000
y=80000÷2000
y=4000
80000÷4000=4000-2000
2000=2000
80000: y=4000-2000
80000:y=2000
y=80000:2000
y=40
12000x=800-30
12000x=770
x=77/1200
80000÷y=4000-2000
80000÷y=2000
y=80000÷2000
y=4000
80000÷4000=4000-2000
2000=2000