#### Answer

Mental math is preferred because the equation is simple enough to easily solve with mental math. Creating the table takes more time than mental math in this case.
x=9

#### Work Step by Step

Use mental math. What number can be added to 4 to equal 13? $9+4=13$
You can use a table to find the value.
$\underline{x}\ \ \ \ \underline{x+4}$
$1\ \ \ \ \ \ \ \ 5$
$2\ \ \ \ \ \ \ \ 6$
$3\ \ \ \ \ \ \ \ 7$
$4\ \ \ \ \ \ \ \ 8$
$5\ \ \ \ \ \ \ \ 9$
$6\ \ \ \ \ \ \ \ 10$
$7\ \ \ \ \ \ \ \ 11$
$8\ \ \ \ \ \ \ \ 12$
$9\ \ \ \ \ \ \ \ 13\longrightarrow$ the solution is 9