A boutique owner sells a salt scrub that is made of a tropical oil blend costing $7.95 per ounce and sea salt costing $1.45 per ounce. The salt scrub ultimately costs $3.40 per ounce. In order to make a new batch of the salt scrub, she just ordered 6 ounces of the tropical oil blend. How many ounces of sea salt will she need to make the salt scrub with the correct proportions?