d=drinks
p=pretzels
1st eq. 3d+3p=9.00
2nd eq. 4d+2p=8.50
multiply 1st eq by 2
6d+6p=18.00
multiply
2nd eq by 3
12d+6p=25.50
subtract
-6d=-7.50
d=1.25
3p=9.00-3d
3p=9-3.75
3p=5.25
p=1.75
price of a pretzel=$1.75
price of a drink = $1.25