Algebra 2 (1st Edition)

$108$ cards.
Given the rule for the number of cards in the n-th row in example 6, $a_{n}=3n$, The formula for the sum of a finite series is $S_{n}=n\displaystyle \cdot\frac{a_{1}+a_{n}}{2}$. We first find $a_{1}$ and $a_{8}$. $a_{1}=3\cdot 1=3$ $a_{8}=3\cdot 8=24.$ Substitute these values into the formula for $S_{8}$. $S_{8}=8\displaystyle \cdot\frac{3+24}{2}=4\cdot 27=108$