I need help with this question, please provide the equation/steps used to get answer

Alpine Thrills Ski Company recently expanded its manufacturing capacity. The firm will now be able to produce up to 27,000 pairs of cross-country skis of either the mountaineering model or the touring model. The sales department assures management that it can sell between 21,000 and 25,000 units of either product this year. Because the models are very similar, the company will produce only one of the two models. The following information was compiled by the accounting department. Model Mountaineering $144.00 85.30 Selling price per unit Variable costs per unit Touring $132.00 85.30 Fixed costs will total $602,400 if the mountaineering model is produced but will be only $511,200 if the touring model is produced. Alpine Thrills Ski Company is subject to a 25 percent income tax rate. Problem 7-51 Part 2 2. If Alpine Thrills Ski Company desires an after-tax net income of $39,120, how many pairs of touring skis will the company have to sell? (Do not round intermediate calculations. Round your final answer to the nearest whole unit.) Number of pairs to be sold units