What was the price of one drink? and what was the price for one pretzel?

D for drinks
p for pretzel

3d + 3p = 9
3d = 9 -3p
d = 3 - p

replace d = 3 - 9 into 4d + 2p = 8.5
4d + 2p = 8.5
4(3 - p) + 2p = 8.5
12 - 4p + 2p = 8.5
-2p = 8.5 - 12
-2p = -3.5
p = 1.75

 the price for one pretzel was $1.75

The sodas are $1.50 and the pretzels are $1.25

X=3 and y=4 is the answer

All you have to do is multiply