Answer
d=30
Work Step by Step
$d-9=21$ $\longrightarrow$ addition property
$d-9+9=21+9$ $\longrightarrow$ simplify
$d=30$
Substitute to check.
$30-9=21$
$21=21\checkmark$
Prealgebra (7th Edition)
by Martin-Gay, Elayn
Published by
Pearson
ISBN 10:
0321955048
ISBN 13:
978-0-32195-504-3
Chapter 2 - Section 2.6 - Solving Equations: The Addition and Multiplication Properties - Exercise Set - Page 148: 11
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