What observed rotation is expected when a 1.5 M solution of (R)-2-butanol is mixed with an equal

Question:

What observed rotation is expected when a 1.5 M solution of (R)-2-butanol is mixed with an equal volume of a 0.75 M solution of racemic 2-butanol, and the resulting solution is analyzed 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.