Answer: To find the residual at 28, you first need to have an equation for your line of best fit (trend line).
If you use two points to find your line, one such equation could be y = -1.5x + 87.
To find the residual, first input the value of x = 28 into the equation. The resulting output is 45.
The value shown in the chart for 28 is only 42. So the residual is -3.
42 - 45 = -3
