In a science experiment, the temperature of a substance is changed from 42°F to 78°F at an average rate of 12 degrees per hour. Over how many hours does the change take place?

78 - 42 = 36

36/12 = ?

To find out the number of hours it takes for the temperature change to occur, we can use the formula:

Number of hours = (Final temperature - Initial temperature) / Average rate of change

Given:
Initial temperature = 42°F
Final temperature = 78°F
Average rate of change = 12°F per hour

Substituting these values into the formula:

Number of hours = (78°F - 42°F) / 12°F per hour
= 36°F / 12°F per hour
= 3 hours

Therefore, the change in temperature takes place over 3 hours.