1. The problem is to solve the equation $60 + \text{———} = 70$ where the missing number is unknown. 2. To find the missing number, we can rewrite the equation as $60 + x = 70$, where $x$ is the unknown. 3. To isolate $x$, subtract 60 from both sides: $60 + x - 60 = 70 - 60$. 4. Simplifying both sides gives $x = 10$. 5. So, the missing number is 10, because $60 + 10 = 70$.