To determine when the equation
\[ -5 = \frac{4 - 3x}{4 - 3x} \]
is undefined, we need to see when the denominator equals zero, as division by zero is undefined.
The denominator in this case is \(4 - 3x\). We set this equal to zero:
\[ 4 - 3x = 0 \]
Now, we solve for \(x\):
\[ 3x = 4 \] \[ x = \frac{4}{3} \]
This means the equation is undefined when \(x = \frac{4}{3}\).
From the provided options, the correct response is:
43
(Which represents \( \frac{4}{3} \))