Speed problem with current(Resolved)

[opus]

Hi I'm trying to solve this problem, but I can'T get the solution exempt by try and error. What am I doing wrong?

Problem:

A ship travels along a river from A to B and back. Time required for both ways is 11,5 hrs. The river has a current of 2,5 Knots(Nm/hr). The distance from A to B is 91 Nm.
What's the speed of the ship (speed thru water!)

I have:
T1= Time to travel from A to B (with the current)
T2= Time to travel from B to A (against the current)
V= Speed of Ship (Speed thru the water)
T2=11,5 hrs -T1
The equation is:
2*91= T1*(V+2,5) + (11,5-T1)*(V-2,5)

I can convert this one back and for, but T1 and V will allways be in there. How would I get the correct value for V?

Note 15,8 is not the coorect one, this one would assume no current and T1=T2!
By try and error I got 16,2 Kn