(30-15b):(-3)=

To simplify the expression \((30 - 15b) : (-3)\), we can rewrite it as \(\frac{30 - 15b}{-3}\).

Now, we can separate the terms in the numerator:

\[ \frac{30}{-3} - \frac{15b}{-3} \]

Calculating each term:

1. \(\frac{30}{-3} = -10\)
2. \(\frac{-15b}{-3} = 5b\)

Now, putting it all together:

\[ -10 + 5b \]

Thus, the simplified expression is:

\[ 5b - 10 \]