Hi Krimi! Remember that in a redox reaction there is always reduction and oxidation occurring simultaneously--if one reaction is a reduction reaction, the other must be an oxidation reaction. To determine which reaction will be which, compare the reaction potentials (reduction potentials in this case). Here we can see that silver has a more positive reduction potential, meaning that it is a more favorable reaction than the tin reduction reaction. Therefore, silver would be reduced and tin would be oxidized. To make the tin reaction an oxidation one, simply flip it and multiply the cell potential by -1. Cell potentials do not change with the number of moles/electrons so for example the silver reduction reaction will always have a reduction potential of 0.80 V.
Ecell = Eox + Ered = 0.14 + 0.80 V = 0.94 V --> this is the standard cell potential
Then you would use the Nernst equation to calculate the cell potential because the concentrations in the cells are not 1 M. Q would be 1.8M/0.055M, and n would be 2 because two electrons "cancel" in the overall reaction. I hope this helps!
