Percentage calculation from negative numbers

QUESTION 1:
Calculating 10% of a Total. If the Total is negative, the Output should be set to "0". How to set this in formula?
Tried SUMIF, but without success.

QUESTION 2:
Percentage calculation when the number is negative. Can't make it to work.
Now have a formula: =SUM(-E14*$E$15) E14 is the negative number, had to add "-" sign in front of it to make it work, but this can't be the solution.
What is?

Example file enclosed. Any help ?

E8:

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E16: 10% of negative is negative?

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If it does not work, what is your expected output of E16?