|-3| means "the absolute value of 3", which is a way of saying how far away from zero the number -3 is on the number line.
The definition of absolute value goes like this:
In other words, if the number
inside the absolute value bars is already positive or zero, we leave it alone. If instead
is negative, we multiply it by -1 to recover the positive version of that number.
Since -3 is negative, it follows that |-3| = -(-3) = 3. So the expression 3 |-3| is equivalent to 3 • 3 = 3² = 9.