To find the amount of change in temperature every hour, you can set up the equation as follows:
\[ 5x = 12 \]
Now, to solve for \(x\), divide both sides of the equation by 5:
\[ x = \frac{12}{5} \]
Calculating this gives:
\[ x = 2.4 \]
Thus, the temperature decreased by 2.4° every hour.