Answer
$=12$
Work Step by Step
Recall the following rule:
$-a+b=b-a$
Thus, we obtain:
$= - 9 + 21$
$= 21 - 9$
$= 12$
Elementary Algebra
by Kaufmann, Jerome; Schwitters, Karen;
Published by
Cengage Learning
ISBN 10:
1285194055
ISBN 13:
978-1-28519-405-9
Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.3 - Integers: Addition and Subtraction - Problem Set 1.3 - Page 20: 110
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