The temperature decreased so you would subtract the amount from the original temperature.
The answer would be:
-15 - 10 = -25
There are 2 choices for the first set, and 5 choices for the second set. Each of the 2 choices from the first set can be combined with each of the 5 choices from the second set. Therefore there are 2 times 5 combinations from the first and second sets. Continuing this reasoning, the total number of unique combinations of one object from each set is:
For this case we have that by definition, the equation of the line of the slope-intersection form is given by:

Where:
m: It's the slope
b: It is the cut-off point with the y axis
We have two points through which the line passes:

We found the slope:

Substituting we have:

Thus, the equation is of the form:

We substitute one of the points and find the cut-off point:

Finally, the equation is:

ANswer:

When I did the math I came up as 3.88 but if you have to round up it wound be 4 or 3.9