Calculating observed rotation.?

What observed rotation is expected when a 1.88M solution of (R)-2-butanol is mixed with an equal volume of a 0.94 M solution of racemic 2-butanol, and the resulting solution is yzed in a sample container that is 1 dm long? The specific rotation of (R)-2-butanol is -13.9 degrees mL g^-1 dm^-1