(1600+t):80=60
1600+t=60*80
t=4800-1600
t=3200
2000:f-670=1330
2000:f=1330+670
f=2000:2000
f=1
1300-(d-678)=400
678-d=400-1300
-d=-900-678
d=1578
1600:80+t=600
20+t=600
t=580
(2000-600):f=70
1400:f=70
f=1400:70
f=20
d-(1300-678)=400
d-622=400
d=400+622
d=1022