UNIT 13: ADDITION AND SUBTRACTION LESSON 1:Solve the following. Examples: Do these:

The missing number is $\boxed{\text{93}}$.

2)
The top number is missing. The sign is '+'.

The missing number is $\boxed{\text{1100}}$.

3)
The bottom right number is missing. The sign is '-'.

The missing number is $\boxed{\text{68}}$.

4)
All numbers are given: Top = 91, Bottom left = 91, Bottom right = 2. The sign is '-'.
This problem appears to be an example of a subtraction relationship, similar to the addition examples. However, it does not fit the pattern $V_T - V_L = V_R$ ($91 - 91 = 0 \neq 2$) or $V_T - V_R = V_L$ ($91 - 2 = 89 \neq 91$). Given that all other problems require finding a missing number, and this one has all numbers filled, it's likely an illustrative example that might contain a slight inconsistency or represent a different type of relationship not explicitly defined. Since there is no missing number to solve for, we will proceed to the next problem.

5)
The top number is missing. The sign is '+'.

The missing number is $\boxed{\text{93}}$.

6)
The bottom right number is missing. The sign is '-'.

The missing number is $\boxed{\text{170}}$.

7)
The top number is missing. The sign is '+'.

The missing number is $\boxed{\text{130}}$.

8)
The top number is missing. The sign is '+'.

The missing number is $\boxed{\text{160}}$.

9)
The bottom left number is missing. The sign is '-'.

The missing number is $\boxed{\text{145}}$.

10)
The top number is missing. The sign is '+'.

The missing number is $\boxed{\text{115}}$.