Marie heated water in a beaker. When she began, the water had a temperature of 40 degrees, and she heated it at a rate of 2.5 degrees per minute. Kathy heated water in a different beaker. When she began, the water had a temperature of 50 degrees, and she heated it at a rate of 1.5 degrees per minute. Which equation could be used to determine how many minutes passed before the water temperature in both beakers was the same?