Mrs. Rini will buy shirts and pants to resell with the purchase price of shirts at Rp. 70.000,00 per piece and the price of pants to Rp. 50,000.00 per piece. The number of shirts and pants purchased is a maximum of 60 pieces and the capital owned is Rp. 20,000,000.00. Formulate the above problem in the form of a mathematical model!