A ferry takes 90 minutes to travel a specific distance while moving downstream along a river. Provided that the speed of the ferry in calm water and the speed of the current are in the ratio of 3: 1, calculate the time required for the ferry to travel the exact same distance upstream.

The correct option is 3 hours.

Step-by-step explanation:

1. Express the speeds using the given ratio:
The ratio of the speed of the ferry in calm water to the speed of the current is 3 : 1.
Let the speed of the ferry in calm water be $v_f=3x$ and the speed of the current be $v_c=1x$, where $x$ is a positive constant.

2. Calculate the downstream speed:
When moving downstream, the ferry travels in the direction of the river current, so the effective speed is the sum of both speeds:
$v_{\text{down}}=v_f+v_c=3x+x=4x$

3. Determine the distance traveled:
The ferry takes 90 minutes to travel downstream. Converting 90 minutes into hours gives:
$90\text{minutes}=\frac{90}{60}=1.5\text{hours}$
Using the formula $\text{Distance}=\text{Speed}\times \text{Time}$:
$d=4x\times 1.5=6x$

4. Calculate the upstream speed:
When moving upstream, the ferry travels against the river current, so the effective speed is the difference of both speeds:
$v_{\text{up}}=v_f-v_c=3x-x=2x$

5. Calculate the time required to travel upstream:
Using the formula $\text{Time}=\frac{\text{Distance}}{\text{Speed}}$:
$t_{\text{up}}=\frac{6x}{2x}=3\text{hours}$

Therefore, the time required for the ferry to travel the exact same distance upstream is 3 hours.