What is the slope of the line between (6,9) and (18, -2 )?
The gradient is
As it is a negative slope it shows that it's gradient is downwards as you move from left to right.
Put in simple terms: It is the amount of 'up or down' for one along.
Let the gradient (slope) be m
Note the positive gradient is an upwards slope whilst a negative gradient is a downward one.
The negative 2 has been highlighted in blue. Subtracting or adding negative numbers needs a bit more care!
It is more precise to keep this as a fraction.