A line has a slope of - 3 and a rise of 21, what is the run?

The run is - 7.

Step-by-step explanation:

Since we know that slope = rise/run, we can calculate the run by inputting the given numbers.

So,

-3 = 21/x and we need to solve for x.

When we cross multiply we get - 3x=21.

Then, divide - 3 on both sides and x = - 7