X - 3 = 7
add 3 to both sides
x - 3 + 3 = 7 + 3
x = 10
addition property of equality
Answer: the average rate of change is 4.
Step-by-step explanation:
The average rate of change is the slope. Therefore, you must use the following formula for calculate the slope:

As you can see in the table, when x=5, y=-2 and when x=9, y=14. Then the points you must substitute into the formula are:
(5,-2) and (9,14)
Then, you obtain:

Yes, the rules of scientific notation are:
1. All non-zero digits are significant
2. Zeros in between non-zeros are significant.
3. Zeros to the left of the first non-zero number are NOT significant.
4. Zeros to the right of non-zero numbers are significant IF a decimal point is present.
P.S: if you need help with sig fig rounding, let me know.