At RATE of RS 18.80 per kg he must sell the MIXTURE of two tea to gain 15%Explanation:Given that:A trader purchases 70 kg of tea at 15 per kg. And 30 kg of tea at 18.50 per kg. Formula: Total cost = Rate × WeightFinding the cost of 70 kg of tea: → Cost of 70 kg of tea = Rs 15 × 70→ Cost of 70 kg of tea = Rs 1050Finding the cost of 30 kg of tea:→ Cost of 30 kg of tea = Rs 18.50 × 30→ Cost of 30 kg of tea = Rs 555Finding the cost of tea when both are mixed:(70 + 30) kg of tea Cost = Rs (1050 + 555)→ 100 kg of tea cost = Rs 1605Given: The packing charges are 2 percent. → Total cost price of tea = Rs (1605 + 2% of 1605) → Total cost price of tea = Rs (1605 + 32.10) → Total cost price of tea = Rs 1637.10To find:At what price he must sell the mixture of two to gain 15%.Formula used:SELLING price = (100 + gain)% of Cost priceFinding the selling price of 100 kg of tea:→ Selling price of 100 kg of tea = Rs (100 + 15)% of 1637.10→ Selling price of 100 kg of tea = Rs (115% × 1637.10) → Selling price of 100 kg of tea = Rs 1882.665 ≈ Rs 1880Finding the selling price of 1 kg of tea:Selling price of 100 kg of tea = Rs 1880∴ Selling price of 1 kg of tea = Rs 1880/100∴ Selling price of 1 kg of tea = Rs 18.80