This question looks really tricky, but it's actually just describing a system of equations. We have the equation for the speed of the boat with the current and the speed of the boat against the current. Call the boat speed b and the current speed c:
[tex]b+c=13[/tex]
[tex]b-c=1[/tex]
Then
[tex](b+c)+(b-c)=13+1[/tex]
[tex]2b=14[/tex]
[tex]b=7[/tex]
So the boat's speed is 7 km/h. Find the current's speed by plugging the boat speed back into one of the original equations:
[tex]7+c=13[/tex]
[tex]c=6[/tex]
The current's speed is 6 km/h.
