A merchant mixes three varieties of rice costing Rs.40/kg, Rs.48/kg and Rs.60/kg and sells the mixture at a profit of 40% at Rs.60 / kg. How many kgs of the second variety will be in the mixture if 4 kgs of the third variety is there in the mixture? a) 1 kg b) 20 kgs c) 3 kgs d) 6 kgs e) 8kgs