Use the Nernst equation which is:
E = E° - (RT/nF)*Ln Q
Where:
E the cell voltage in V,
R the gas constant 8.314 J/K•mol,
T the room temperature normally taken 298.15K, n=3 in this case,
F the Faraday constant 96485C,
Ln is the operation of natural logarithm, and: Q = [Cl-]^3*[Al3+]
Plugging in our values, will give us:
E = 1.88-(8.314*298.15/(3*96485))*Ln(0.010^3...)
= 2.01 (V)