Solution: Let [tex]x[/tex] be the number of birds and [tex]y[/tex] be the number of cats.
[tex]x+y=29 \implies y=29-x[/tex]
[tex]3.50 x +6.50 y= 146.50[/tex]
[tex]3.50 x+6.50(29-x)=146.50[/tex]
[tex]3.50x+188.5-6.5x=146.50[/tex]
[tex]3x=188.5-146.50[/tex]
[tex]3x=42[/tex]
[tex]x=\frac{42}{3} =14[/tex]
Therefore, there were 14 birds at the shelter on Friday
