To do this topic, you need to know long subtraction and estimated subtraction.
To review the Long Subtraction topic, see here.
To review the Estimated Subtraction topic, see here.

Example 1:

Subtract and Estimate.

$9.02 - $3.55

Answer Estimate

Part 1: Calculate the answer
Use long addition to calculate the answer.

$9.02 - $3.55 $5.47

Part 2: Estimate the answer
Estimate each addend to the correct place value and add.
In this problem, we round to the nearest dollar value.   $9.00

$9.02	rounds to
- $3.55	rounds to	- $4.00   $5.00

Answer   Estimate