ANSWER:
3 shirts
STEP-BY-STEP EXPLANATION:
We can calculate the number of t-shirts purchased through a system of equations. Let x be the number of t-shirts and y be the number of jeans, we establish the following:
[tex]\begin{gathered} 12x+45y=261 \\ \\ \:x+y=8\rightarrow y=8-x \end{gathered}[/tex]We substitute the second equation into the first and solve for x, just like this:
[tex]\begin{gathered} 12x+45(8-x)=261 \\ \\ 12x+360-45x=261 \\ \\ -33x=261-360 \\ \\ x=\frac{-99}{-33} \\ \\ x=3 \end{gathered}[/tex]Therefore, Beth bought a total of 3 shirts.