The temperature dropped 15 degrees from the high temperature to –6° C. What was the high temperature?

15 + (-6) = 9

To find the high temperature, we need to determine the temperature after the drop of 15 degrees.

Let's call the high temperature "x".

From the problem statement, we know the temperature dropped 15 degrees from the high temperature to -6°C.

This can be expressed as an equation:

x - 15 = -6

To solve for x, we will isolate it on one side of the equation by adding 15 to both sides:

x - 15 + 15 = -6 + 15

x = 9

Therefore, the high temperature was 9°C.