Let's use the variable x to represent the cost of one baseball.
If Noah spent a total of $121 in 7 baseball's and a $100 bat, we can write the equation:
[tex]121=7x+100[/tex]Now, solving this equation for x, we have:
[tex]\begin{gathered} 7x=121-100 \\ 7x=21 \\ x=\frac{21}{7} \\ x=3 \end{gathered}[/tex]So the cost of each baseball is $3.