A T-shirt maker has machines to make shirts with both heat-transfer and silkscreens. The heat-transfer shirts take an average of 15 minutes to make, but are sold for $10 each, while the silkscreen shirts take about 30 minutes, and can be sold for $35. If during busy times, the shirt maker earns an average of $50 an hour, what is the ratio of heat-transfer shirts sold to silkscreen shirts sold?