I was confused at first until I realized that you'd shared not one, not two, but three questions in one post. would you please post just one question at a time to avoid this.
I'll focus on your second question only: Solve 3 + |2x - 4| = 15.
Subtr. 3 from both sides. Result: |2x - 4| = 12
Divide all terms by 2, to reduce: |x - 2| = 6
Case 1: x-2 is already +, so we don't need | |:
x - 2 = 6 => x = 8 (first answer)
Case 2: x-2 is negative, so |2x-4| = -(2x-4) = 6
Then -2x + 8 = 6. Subtr. 8 from both sides: -2x = -2
Div both sides by -2: x = 1 (second answer)
Be sure to check these results by subst. them into the original equation.
Please post your other questions separately. Thanks and good luck!