How to calculate transmittance from concentration?

Im not sure how to do these 3. A 10 mM solution has a transmittance of 45%. Calculate the transmittance of a 20mM solution at the same wavelength and optical pathlength. 4. Two colored solution, C and D contain different dyes. Let the transmittances of these two solutions be TC and TD respectively, when... show more Im not sure how to do these

3. A 10 mM solution has a transmittance of 45%. Calculate the transmittance of a 20mM solution at the same wavelength and optical pathlength.

4. Two colored solution, C and D contain different dyes. Let the transmittances of these two solutions be TC and TD respectively, when measured in a 1-cm cell at a given wavelength. Express the transmittance TCD of the mixture of equal volumes of C and D, measured under the same conditions, in terms of TC and TD.
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