As you become more comfortable with reading and writing mathematical expressions, you might notice they are useful for seeing the amount you start with and what you're subtracting.
Any subtraction problem can be turned into a written expression. For instance, let's say your tomato plant has seven tomatoes and you pick four. To figure out the number of tomatoes that are left on the plant, you might write an expression like this:
7 - 4
The expression is just another way of describing the situation: seven tomatoes minus four that were picked.
Write these situations as mathematical expressions. Don't solve the problems yet — simply set them up.
You have a pie with eight pieces. You eat two pieces.
You have nine cans of soup and you donate seven to the food bank.
You've gathered six sticks for your campfire. You throw three sticks on the fire.