(1600+t):80=60
1600+t=60*80
1600+t=4800
t=4800-1600
t=3200
--------------
(1600+3200):80=60
60=60
2000:f-670=1330
2000:f=1330+670
2000:f=2000
f=2000/2000
f=1
------------------------
2000:1-670=1330
1330=1330
1300-(d-678)=400
d-678=1300-400
d-678=900
d=900+678
d=1578
--------------------------
1300-(1578-678)=400
400=400