Let's use the variable x to represent the number of jeans and y to represent the number of t-shirts.
The price paid for x jeans is 20x and the price paid for y t-shirts is 10y.
If the total cost is $350, we can write this equation:
[tex]\begin{gathered} 20x+10y=350 \\ 2x+y=35 \end{gathered}[/tex]The number of items is 25, so we can write a second equation:
[tex]x+y=25[/tex]Subtracting the first and second equations, we have:
[tex]\begin{gathered} 2x+y-(x+y)=35-(25) \\ 2x+y-x-y=10 \\ x=10 \end{gathered}[/tex]Now, solving the second equation for y:
[tex]\begin{gathered} x+y=25 \\ 10+y=25 \\ y=25-10 \\ y=15 \end{gathered}[/tex]Therefore she bought 10 pairs of jeans and 15 t-shirts.