Let \( x \) be the number of pages Susan read yesterday. According to the problem, we have the equation:
\[ 17 = 13 - 8 \]
We can rewrite this as:
\[ 17 = 13x - 8 \]
To solve for \( x \), add 8 to both sides:
\[ 17 + 8 = 13x \] \[ 25 = 13x \]
Now, divide both sides by 13:
\[ x = \frac{25}{13} \] \[ x \approx 1.92 \]
However, to maintain integrity with the pages read, we look back at the equation:
\( 13x - 8 = 17 \)
\[ 13x = 17 + 8 \] \[ x = \frac{25}{13} \]
Considering \( 13 \) gives \( 1.92\), we can observe approximate counts for integers. The realization clarifies:
Yesterday’s pages read, \( 25/13\) or another 8 backtracked validate yield \( 25\).
This correctly reads:\[ x = \boxed{25} \] Susan read 25 pages yesterday.