To solve the equation \( 0.9w - 0.5w + 0.1w = 3 \), let's combine like terms on the left side:
\[ (0.9w - 0.5w + 0.1w) = (0.9 - 0.5 + 0.1)w = 0.5w \]
Now we rewrite the equation:
\[ 0.5w = 3 \]
Next, to isolate \( w \), divide both sides by \( 0.5 \):
\[ w = \frac{3}{0.5} = 3 \times 2 = 6 \]
Thus, the solution is:
\[ w = 6 \]