Answer:
-75
Step-by-step explanation:
3(-30)=-90
-90+15 is -75
The speed of the current in a river is 6 miles per hour
<em><u>Solution:</u></em>
Given that,
Speed of boat in still water = 20 miles per hour
Time taken = 3 hours
Distance downstream = 78 miles
To find: Speed of current
<em><u>If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then: </u></em>
Speed downstream = (u + v) km/hr
Speed upstream = (u - v) km/hr
<em><u>Therefore, speed downstream is given as:</u></em>

We know that,
Speed downstream = (u + v)
26 = 20 + v
v = 26 - 20
v = 6 miles per hour
Thus speed of the current in a river is 6 miles per hour
21x-9+6y
combining terms: 4x+17x=21x
Answer:
B
Step-by-step explanation: