128:(42+17)

To solve the expression \( 128:(42+17) \), we first need to simplify the expression inside the parentheses:

\[ 42 + 17 = 59 \]

Now, we can rewrite the expression as:

\[ 128 : 59 \]

This represents the division of 128 by 59.

Calculating this, we have:

\[ 128 \div 59 \approx 2.169 \]

Therefore, the result is approximately \( 2.169 \).