x( 1- 13%)( 1-7%)= 1，
So x =1÷ (0.87× 0.93) ≈1.236.
That is, the finished product needs 1 kg of raw materials 1.236 kg. On this basis, the sum of 8,000 yuan of raw materials and 1200 yuan workers' wages is 9,200 yuan, and the cost is1.236× 9200 =11.2 yuan.
The formula is: cost = 1÷( 1- moisture content) ÷( 1- loss rate) × (unit price of raw materials+unit salary of workers) (unit: yuan/kg).