Given the expression;
(3+8x)+7x
First thing we need to do is open up the parenthesis as shown;
[tex]\begin{gathered} =(3+8x)+7x \\ =\text{ 3+8x+7x} \end{gathered}[/tex]
Simplify by adding up the like terms as shown;
[tex]\begin{gathered} =\text{ 3 + 8x + 7x} \\ =\text{ 3 + 15x} \end{gathered}[/tex]
Hence option A is correct
