simultaneous equations

1) 2 cans of tomato soup and 3 cans of corn soup are sold at $47.5, while 4 cans of tomato soup and 1 can of corn soup are sold at $42.5.
a) Let $x be the selling price of a can of tomato soup and $y be the selling price of a can of corn soup. The simultaneous equations in x and y are
2x + 3y = 47.5.....(1)
4x + y = 42.5.....(2)
b) What are the respective selling prices of a can of tomato soup and a can of corn soup?
(1) * 2:
4x + 6y = 95.....(3)
(3) - (2):
5y = 52.5
y = 10.5
Subst. y=10.5 into (2)
4x + 10.5 = 42.5
4x = 32
x=8
The respective selling prices of a can of tomato soup and a can of corn soup are $8 and $10.5

(2) Last Sunday, Mr. Wong and his family ordered 5 dishes of dim-sum of medium size and 2 dishes of dim-sum of large size in a restaurant, and the bill was $128. Mr. Ho and his family ordered 8 dishes of dim-sum of medium size and 3 dishes of large size, and the bill was $200. How much did each type of dim-sum cost in the restaurant? (Suppose there were no service charge and no charge for tea.)
Suppose a dish of dim-sum of medium size costs $x, and a dish of dim-sum of large size costs $y, accordingly,
5x + 2y = 128.....(1)
8x + 3y = 200.....(2)
(1) * 3:
15x + 6y = 384.....(3)
(2) * 2:
16x + 6y = 400.....(4)
(4) - (3):
x = 16
Subst. x=16 into (1)
5(16) + 2y = 120
80 + 2y = 120
2y = 40
y = 20
A dish of dim-sum of medium size costs $16, and a dish of dim-sum of large size costs $20, accordingly,