The speed of a boat in still water is 28 mph The boat travel

The speed of a boat in still water is 28 mph. The boat traveled 70 mi down a river in the same amount of time in which it traveled 42 mi up the river. Find the rate of the rivers current.

D=RT
70=(28+R)T
T=70/(28+R)
42=(28-R)T
T=42/(28-R)
70/(28+R)=42/(28-R)
70(28-R)=42(28+R)
1,960-70R=1,176+42R
-70R-42R=1,176-1,960
-112R=-784
R=-784/-112
R=7 MPH IS THE RIVER CURRENT.
PROOF:
70/(28+7)=42/(28-7)
70/35=42/21
2=2