Let the expression we will add be "A", thus we can write:
[tex]5x+7+A=9(x+1)[/tex]We can use the distributive property on the right hand side and then use a bit algebra to solve for "A". The distributive property is shown below:
[tex]a(b+c)=ab+ac[/tex]Let's do the algebra. The steps are shown below:
[tex]\begin{gathered} 5x+7+A=9(x+1) \\ 5x+7+A=9x+9 \\ A=9x+9-5x-7 \\ A=4x+2 \end{gathered}[/tex]Thus, we need to add 4x + 2 to "5x + 7" to make it equal to "9(x+1)".
The correct answer is:
B