The justification for the step taken from line 2 to line 3 is:
Combining like terms on one side of the equation.
Let's detail each step:
Starting with the equation:
[tex]\[ 3x + 9 - 7x = x + 10 + x \][/tex]
First, we combine like terms on each side of the equation:
On the left side:
[tex]\[ 3x - 7x + 9 = -4x + 9 \][/tex]
On the right side:
[tex]\[ x + x + 10 = 2x + 10 \][/tex]
Putting it together we get:
[tex]\[ -4x + 9 = 2x + 10 \][/tex]
So, the correct justification for the step from:
[tex]\[ 3x + 9 - 7x = x + 10 + x \][/tex]
to:
[tex]\[ -4x + 9 = 2x + 10 \][/tex]
is combining like terms on one side of the equation.
