we know that
2 1/2----------> (2*2+1)/2-----------> 5/2
[unit rate of soda to pineapple juice]=[quantity of soda]/[quantity of pineapple]
[unit rate of soda to pineapple juice]=[5/2]/[4/5]----> 25/8-------> 3.125---> 3 1/8
the answer is 3.125 (3 1/8)