A job is scheduled to be completed in 30 weeks with a labour employment of 100 skilled operatives, 40 semi-skilled operatives and 60 unskilled operatives. The standard weekly wages of each type of operatives are - skilled RO 60, semi-skilled RO 36 and unskilled RO 24. The work is actually completed in 32 weeks with a labour force of 80 skilled, 50 semi-skilled and 70 unskilled operatives and the actual weekly wage rates average RO 65 for skilled, RO 40 for semi-skilled and RO 20 for unskilled labour.

Analyse the variance in the labour cost due to various reasons.