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The expression is 

Place value chart for 892 and 645.

Line up the decimal points and draw a line below the numbers.

First find the difference on the ones digit.

Notice that it is not possible to subtract 2 from 5.

 So, 1 unit must be borrowed from tens column.

The difference of the ones digit = 12- 5 = 7.

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Next find difference of the tens digit.

The difference of the tens digit = 8 – 4 = 4

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Next find the difference of the hundreds digit.

The difference of the hundreds digit = 8 – 6 = 2.

The subtraction is 247.