Final answer:
The derivative of the function f(x) = -3x + 7, which is a linear function, is constant and equal to the slope of the function. Therefore, df/dx at x = -1 is -3.
Step-by-step explanation:
To find the derivative of a linear function, we use the power rule. The power rule states that for a function of the form y = axⁿ, the derivative is given by 
dy/dx = naxⁿ⁻¹. 
In this case, the function is 
y = -3x + 7, 
So the derivative is 
dy/dx = -3.
Since we want to find the derivative at x = -1, we substitute -1 into the derivative expression: 
dy/dx = -3. 
Therefore, the derivative of the function at x = -1 is -3.