You have dL = 1/10 L, which is true, but

nL = (1/1,000,000,00)L or 10^-9 L (not 10^-6)

and

mL = (1/1,000)L or 10^-3 L (not 10^-5)

If you got these wrong, you would be lost from the start.

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The number of significan digits in the result of a calculation can have only as many significant digits as the number with least number of significant digits that was used in the calculation.

You can probably find some examples in a special section on measurement or even a section titled "signficant figures" in many texts on chemistry and physics, or you could go online and find it quicker.

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Significant Digits, the problem of zeros:

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A zero between two other digits is always significant.

Zeros to the left of all nonzero digits are not significant, i.e., leading zeros are not significant.

Zeros right of the decimal point and to the right of nonzero digits are significant.

Zeros on integers may or may not be significant, depending on the accuracy of the measurement from which the number was derived.