Answer :
[tex]3x-\ pineapple\\
2x-\ mango\\\\
after\ selling\ 144\ pineapple:\\
3y-\ pineapple\\
5y-\ mango\\\\
3x-144=3y\ \ | add\ 144\\
2x=5y\\\\
3x=3y+144\ \ \ | divide\ by\ 3\\
2x=5y\\\\
x=y+48\\2x=5y\\\\
2(y+48)=5y\\
2y+96=5y\ \ \ | subtract\ 2y\\
96=3y\ \ \ | divide\ by\ 3\\
32=y\\
x=32+48=80\\\\
There\ were\ 240\ pineapple\ muffins.
[/tex]