Cell Potential Questions

Standard electrode potential for ${\text{Sn}}^{4+}/{\text{Sn}}^{2+}$ couple is $+0.15\text{V}$ and that for the ${\text{Cr}}^{3+}/\text{Cr}$ couple is $-0.74\text{V}$. These two couples in their standard state are connected to make a cell. The cell potential will be:

For the reduction of silver ions with copper metal, the standard cell potential was found to be $+0.46\text{V}$ at $25^{\circ }\text{C}$. The value of standard Gibbs energy, $\Delta G^{\circ }$ will be ($F=96500{\text{C mol}}^{-1}$):

A button cell used in watches functions as follows:$\text{Zn}(s)+{\text{Ag}}_2\text{O}(s)+{\text{H}}_2\text{O}(l)\to 2\text{Ag}(s)+{\text{Zn}}^{2+}(aq)+2{\text{OH}}^{-}(aq)$ Given:$E_{{\text{Zn}}^{2+}/\text{Zn}}^{\circ }=-0.76\text{V}$$E_{{\text{Ag}}_2\text{O}/\text{Ag}}^{\circ }=0.34\text{V}$ The cell potential $E_{cell}^{\circ }$ is: