You have to set up a system of equations
x+y=104
3x-y=104
Sodas = 78
Hotdogs = 26
Y=.75x-1 im might be wrong i think im wrong but im not sure
15/40 x 100 = 37.5
equation for percent decrease is diiference/original x 100.
Is it 0.5? if so, the answer is 0.25%
if it is supposed to be just a 5 then the answer would be 2.5%