The variable cost is calculated as -
Sales - Variable cost = Contribution Margin
Given, Contribution Margin = 25 %
Variable cost = 1 - Contribution Margin = 1 - 25 % = 75 %
25 % of Sales = Contribution Margin = $ 400,000
Sales = $ 400,000 ÷ 25 %
Sales = $ 1,600,000
Variable costs = 75% of Sales = 75 % × $ 1,600,000 = $ 1,200,000