the speed of aboat in still water is 15km/hr it needs four more hours to travel 63km against the current of ariver than it need to travel down the river determine the speed of the current of the river

6 m/ s

Step-by-step explanation:

Let the speed of the boat in still water be represented by, Vb

Let speed of the river be Vr.

Let the time taken to travel downstream be t h

=> time taken to travel upstream = (t + 4) h.

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1) While traveling upstream, the speed of the boat becomes equal to the difference of the speed of boat in still water and speed of the river, I.e.,

= Vb - Vr

= 15 - Vr

2) While traveling downstream, the speed of the boat becomes equal to the sum of of speed of boat in still water and speed of the river, I.e.,

= Vb + Vr

= 15 + Vr

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Our golden formula:

Upstream:

Downstream:

solving for t so as to replace it in eqn. (i):

Placing it in eqn. (i)

Getting all variables to the LHS

combining like terms to get the following equation:

eliminating "-":

dividing the whole thing by 2:

factorising:

Either,

Vr = 6

or,

Vr = -37.5 m/ s

Since, it's the speed of the river we're talking about, it can't be negative.

Therefore,

Vr = 6 m/ s

answer is

c) 4

step-by-step explanation: