Answer:
65
Step-by-step explanation:
Answer:
Sry if it is wrong..........
Try this solution:
Answer: 6 & 4.5 (m-per-h)
Step-by-step explanation:
- The basic formula used in this task is S=V*t, where S - distance, V - speed, t - time.
- the downstream speed is: V+Vc, where V - the speed of the boat in still water, Vc - the speed of the current.
- the upstream speed is: V-Vc.
- according to the described above the distance for downstream is S1=(V+Vc)*t1, where t1=10; the distance for upstream is S2=(V-Vc)*t2, where t2=70.
- for whole travel down- and upstream: S=S1+S2.
- Using these it is possible to make up the system of the equations:

V - the speed of the boat in still water - 6 miles per hour, Vc - the speed of the current - 4.5 miles per hour. All the details for the system of the equations are in the attachment.
<span>Changing the grouping of the addends should not change the sum, according to the associative property of addition. You might group them differently with (50 + 3) + 47, so that you have 50 + (3 + 47). You might not regroup them with (16 + 4) + 5 rather than 16 + (4 + 5).</span>