corrected an error in the description of Exercise 1 b)

doc/handbook/3_tutorialcoupled.tex

@@ -368,7 +368,7 @@ For the visualization of the results using ParaView, please refer to section \re
   Change the size of the model domain so that you get a rectangle with
   edge lengths of $\text{x} = \unit[400]{m}$ and $\text{y} = \unit[500]{m}$ and with
   discretization lengths of $\Delta \text{x} = \unit[20]{m}$ and $\Delta
-  \text{y} = \unit[20]{m}$. For this you have to edit the parameter file (\texttt{tutorialproblem\_coupled.input})
+  \text{y} = \unit[20]{m}$. For this you have to edit the parameter file (\texttt{tutorial\_coupled.input})
   and run the program again.\\
   Note, that you do not have to recompile the program if you make changes to the parameter file.