70-(81-39) :7+6*7 - 90:5+85:17

Let's break down the expression step by step:

The expression is: \[ 70 - (81 - 39) : 7 + 6 * 7 - 90 : 5 + 85 : 17 \]

1. Calculate the parentheses: \[ 81 - 39 = 42 \]

2. Rewrite the expression: \[ 70 - 42 : 7 + 6 * 7 - 90 : 5 + 85 : 17 \]

3. Perform the divisions: \[ 42 : 7 = 6 \] \[ 90 : 5 = 18 \] \[ 85 : 17 = 5 \]

4. Rewrite the expression: \[ 70 - 6 + 6 * 7 - 18 + 5 \]

5. Calculate \(6 * 7\): \[ 6 * 7 = 42 \]

6. Rewrite the expression: \[ 70 - 6 + 42 - 18 + 5 \]

7. Perform the additions and subtractions from left to right:

   • First, \(70 - 6 = 64\)
   • Then, \(64 + 42 = 106\)
   • Next, \(106 - 18 = 88\)
   • Finally, \(88 + 5 = 93\)

The final result is: \[ \boxed{93} \]