#### Answer

$-5$

#### Work Step by Step

RECALL:
$a-b = a+ (-b)$
Thus,
$8-13 \\= 8+(-13)$
The numbers being added have different signs.
To find the sum, perform the following steps:
(1) Subtract the bigger absolute value by the smaller absolute value to obtain:
$|-13| - |8| = 13 - 8 = 5$
(2) The sum will have the same sign as the number with the bigger absolute value.
Since $|-13| \gt |9|$, then the sum is negative.
Thus,
$8-13 = 8+(-13)=-5$