Answer:
The answer to your question is: yield = 56.27%
Explanation:
Data
       CH3CH2CH2CH2OH (l) → CH3 CH2CH2CH2Br
        18.54 ml 1-butanol       15.65 g of 1-bromobutane
% yield = ?
density = 0.81 g/ml
MM = 74 g  1- butanol
MM = 137 g 1-bromobutane
Process
Calculate mass of 1- butanol
       density = mass/volume
       mass = density x volume
       mass = 0.81 x 18.54
       mass = 15.02 g of 1-butanol
Theoretical yield
       74 g of 1- butanol -----------------  137 g of 1-bromobutane
       15.02 g of 1- butanol -------------  x
       x = (15.02 x 137) / 74
       x = 27.81 g of 1-bromobutane
% yield = experimental yield / theoretical yield x 100
% yield = 15.65 / 27.81 x 100
% yield = 56.28