1. 4 3 9 H T U What is the most significant figure in
The most significant figure is in the hundreds column ...
... so round to the nearest hundred.

2. 439 is between 400 and 500.
400
450
500
439
It is closer to 400 than 500.
So we get 400 when we round 439 to the nearest hundred.
We get 400 when we round 439 to one significant figure.

3. 5 8 0 7 TH H T U What is the most significant figure in
The most significant figure is in the thousands column ...
... so round to the nearest thousand.

4. 5807 is between 5000 and 6000.
5000
5500
6000
5807
It is closer to 6000 than 5000.
So we get 6000 when we round 5807 to the nearest thousand.
5807 rounded to one significant figure is 6000.

5. 9 7 3 H T U What is the most significant figure in
The most significant figure is in the hundreds column ...
... so round to the nearest hundred.

6. 973 is between 900 and 1000.
900
950
1000
973
It is closer to 1000 than 900.
So we get 1000 when we round 973 to the nearest hundred.
973 rounded to one significant figure is 1000.

7. 1 5.8 T U 1/10 What is the most significant figure in
The most significant figure is in the tens column ...
... so round to the nearest ten.

8. 15.8 is between 10 and 20. 10 15 20
15.8
It is closer to 20 than 10.
So we get 20 when we round 15.8 to the nearest ten.
15.8 rounded to one significant figure is 20.