I have this mathematical problem, and I don't know how to tackle it.
Total price of a jacket and shoes is $106$ euros.
The shoes cost $13$ more euros than the jacket.
How much does the jacket cost?
$S+J=106$
$S=J+13$
$J=?$
Is the question missing something?
With this question, can't the price of the jacket can be anything, or am I mistaken?
You want to solve the system $$j+s=106,\,s=j+13$$ for $j,$ with the variables standing for the obvious quantities.
This is a linear system of the form $x+y=a,\,x-y=b.$ This always has a unique solution.