15.6 + 2(x - 3.4)
You'll begin by expanding the parenthesis with the number just in front of it, which is 2
15.6 + [(2*x) - (2*3.4)]
15.6 + 2x -6.8
Re-arranging the terms now gives you this;
15.6 - 6.8 + 2x
8.8 + 2x OR
2x + 8.8
**Note that when positive 2 multiplies the negative 3.4, the result is a negative 6.8**