1. **State the problem:** Simplify the expression $99:(45-39+5)-25:5$. 2. **Understand the notation:** The colon ":" here represents division. So the expression is $\frac{99}{45-39+5} - \frac{25}{5}$. 3. **Calculate the denominator in the first fraction:** $$45 - 39 + 5 = 6 + 5 = 11$$ 4. **Rewrite the expression with calculated denominator:** $$\frac{99}{11} - \frac{25}{5}$$ 5. **Perform the divisions:** $$\frac{99}{11} = 9$$ $$\frac{25}{5} = 5$$ 6. **Subtract the results:** $$9 - 5 = 4$$ **Final answer:** $4$