A margin of 25% means that the profit is 25% of the selling price.
Therefore for every $100 selling price, the profit will be $25, and therefore the cost will be $75 (which is 75% of the selling price).
If the cost is $100,000, and if this is to be 75% of the selling price, then the selling price must be 100,000 / 75% = $133,333.
(If the question simply refers to ‘margin’ then this is automatically a % of the selling price. If the question ever says ‘a margin of 25% on cost’ then in this case only, the profit would be 25% of the cost.)