To solve the equation \( -\frac{x}{2.9} = -3 \), you can start by eliminating the negative signs on both sides:
\[ \frac{x}{2.9} = 3 \]
Next, multiply both sides of the equation by \( 2.9 \) to isolate \( x \):
\[ x = 3 \times 2.9 \]
Now calculate the right side:
\[ x = 8.7 \]
So, the solution to the equation is:
\[ \boxed{8.7} \]