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7.
Refer to: http://www2.ucdsb.on.ca/tiss/stretton/database/Standard_Reduction_Potentials.htm
Al³⁺(1.0 M) + 3e⁻ → Al(s)   E° = -1.66 V
Pb²⁺(1.0 M) + 2e⁻ → Pb(s)   E° = -0.13 V
(Reduction potentials from different sources may be slightly different.)

At standard state:
2Al(s) + 3Pb²⁺(1.0 M) → 2Al³⁺(1.0 M) + 3Pb(s)   Ecell°
Ecell° = E°(red) - E°(oxid) = (-0.13) - (-1.66) = +1.53 V

Now,
2Al(s) + 3Pb²⁺(0.1 M) → 2Al³⁺(0.01 M) + 3Pb(s)   Ecell
Nernst equation:
Ecell = Ecell° - {RT/(nF)} ln{[Al³⁺]²/[Pb²⁺]³}
Ecell = +1.53 - {8.314 × 298 / (6 × 96485)} ln(0.01²/0.1³)
Cell potential, Ecell = +1.54 V

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8.
Refer to: http://www2.ucdsb.on.ca/tiss/stretton/database/Standard_Reduction_Potentials.htm
Cu²⁺(1.0 M) + 2e⁻ → Cu(s)   E° = +0.34 V
Ag⁺(1.0 M) + e⁻ → Ag(s)   E° = +0.80 V
(Reduction potentials from different sources may be slightly different.)

When Ag as the cathode, at standard state:
Cu(s) + 2Ag⁺(1.0 M) → Cu²⁺(1.0 M) + 2Ag(s)   Ecell°
Ecell° = E°(red) - E°(oxid) = (+0.80) - (+0.34) = +0.46 V

Now,
Cu(s) + 2Ag⁺(? M) → Cu²⁺(0.1 M) + 2Ag(s)   Ecell = +0.1 V
Nernst equation:
Ecell = Ecell° - {RT/(nF)} ln([Cu²⁺]/[Ag⁺]²)
+0.1 = +0.46 - {8.314 × 298 / (2 × 96485)} ln(0.10/[Ag⁺]²)
0.01284 ln(0.10/[Ag⁺]²) = 0.36
ln(0.10/[Ag⁺]²) = 28.04
0.10/[Ag⁺]² = e²⁸˙⁰⁴
[Ag⁺] = √(0.10/e²⁸˙⁰⁴)
[Ag⁺] = 2.6 × 10⁻⁷ M