Question

find-(-x) when x is 6

Answer 1

Essentially what -(-x) means is -1 times -x, and minus times minus is a positive, so this equals positive x, which is simply 6 in this example!

Answer 2

Negative of a negative is a positive because a product of an even number of negative factors is always positive.

Answer 3

Just substitute the value you were given in the expression you were given:
-(-x) = -(-6) = 6
Think of -x as the opposite of x. The opposite of 6 is -6. The opposite of -6 is 6.
Here you were taking the opposite of the opposite of 6, which is the opposite of -6 which is 6.