In a science experiment, the temperature of a substance is changed from 42°F to -54°F at an average rate of -12 degrees per hour. Over how many hours does the change take place?

**Write as an expression and solve
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(-54-42)° / (-12°/hr) = -84/-12 = 7 hr

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

(change in temperature) / (rate of change) = number of hours

Given:
Initial temperature = 42°F
Final temperature = -54°F
Rate of change = -12°F/hour

Let's plug these values into the formula:

(change in temperature) = (final temperature) - (initial temperature)
(change in temperature) = (-54°F) - (42°F)
(change in temperature) = -96°F

(number of hours) = (change in temperature) / (rate of change)
(number of hours) = -96°F / (-12°F/hour)
(number of hours) = 8 hours

Therefore, the temperature change from 42°F to -54°F takes place over 8 hours.

42--54=

--=turn both into a positive
Add normal
42+54=94
Which is 7 hours