How to subtract numbers
To subtract numbers from each other you can use a variety of written methods such as the column method, or a number line; or you could use a mental arithmetic method.
Resources for physically subtracting numbers together could include: an abacus, Cuisinaire rods, Numicon or Base 10.
Try using more than one method and practice checking your answers with a calculator.
Government guidelines (Year 4  6) Pupils should be taught to:

Subtraction worksheets  Year 6 Primary maths resources, activities and worksheets
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Subtracting from numbers, up to 10,000,000