What is the justification for the step taken from line 2 to line 3? 5 lines of math. The first line has, 3 x plus 9 minus 7 x equals x plus 10 plus x. The second line has, negative 4 x plus 9 equals 2 x plus 10. An arrow pointing from the front of the second line to the front of the third line. The third line has, negative 6 x plus 9 equals 10. The fourth line has, negative 6 x equals 1. The last line has x equals negative StartFraction 1 Over 6 EndFraction. the subtraction property of equality the multiplication property of equality combining like terms on one side of the equation the distributive property