Short Answer 
The problem involves defining the current’s speed (x) and the sea lion’s modified speeds while moving with and against the current. By setting the times for both scenarios equal and solving the resulting equation, we find that the speed of the current is 2.5 km/hr.
Step 1: Define the Variables
To solve the problem, we start by defining the variables involved. Let x be the speed of the current in km/hr. The sea lion’s speed when moving with the current becomes 15 + x, while moving against the current, it becomes 15 – x. These adjustments account for the influence of the current on the sea lion’s natural speed.
Step 2: Establish the Equations
Next, we establish the equations based on the information given. The total distance traveled with the current is 35 km, and against the current is 25 km. The times taken for both scenarios can be represented as follows:
- Time with the current: 35/(15 + x)
- Time against the current: 25/(15 – x)
Setting these two expressions equal allows us to create one equation to solve for x.
Step 3: Solve the Equation
Now, we can solve the equation derived from equating the two time expressions. The equation can be simplified to:
- 35/(15 + x) = 25/(15 – x)
- Cross-multiplying gives us: 150 – 60x = 0
After simplifying, we find x = 2.5 km/hr, indicating the speed of the current. This concludes the problem-solving process.