Answer:
8.4
Explanation:
To find the numerical value of the expression, put the values where the letters are and do the arithmetic.
Substitute
|3 -2(-4.2)| -3
Evaluate
|3 +8.4| -3 . . . . perform the multiplication
11.4 -3 . . . . . . . absolute value of a positive number changes nothing
8.4 . . . . . . . . . perform the sum
The value of the expression is 8.4.
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Additional comment
If you really need help with this, you can put the formula into a calculator or spreadsheet and let it do the arithmetic.