To evaluate the expression \(-3uv\) for \(u = -1\) and \(v = -4\), we can substitute the values of \(u\) and \(v\) into the expression.
\[ -3uv = -3(-1)(-4) \]
Now, calculate the product:
\[ = -3 \times -1 \times -4 \]
Calculating \(-3 \times -1\) first:
\[ -3 \times -1 = 3 \]
Next, multiplying \(3\) by \(-4\):
\[ 3 \times -4 = -12 \]
Thus, the final result is:
\[ -3uv = -12 \]
So, the value of the expression is \(-12\).