#### Answer

$d=x+2y$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To find the common difference of the given arithmetic sequence, $
x+3y,2x+5y,3x+7y
,$ subtract a term by its previous term.
$\bf{\text{Solution Details:}}$
Since the common difference of an arithmetic sequence is the difference between a term and its previous term, then with $a_2=
2x+5y
$ and $a_1=
x+3y
$, the common difference, $d$, is
\begin{array}{l}\require{cancel}d=a_2-a_1\\\\
d=2x+5y-(x+3y)
\\\\
d=2x+5y-x-3y
\\\\
d=(2x-x)+(5y-3y)
\\\\
d=x+2y
.\end{array}