Question 90980
Let cost of each burger = $x and cost of each fry = $y.
Then three burgers and four fries cost = $(3x + 4y).
This value is equal to $16.80.


3x + 4y = 16.80 ________(1)


Also, two burgers and six fries cost = $(2x + 6y).
This value is equal to $17.20.


2x + 6y = 17.20 ________(2)


Multiplying both sides of equation (1) by 2
6x + 8y = 33.60 ________(3)


Multiplying both sides of equation (2) by 3
6x + 18y = 51.60 ________(4)


Subtracting both sides of equation (3) from the respective sides of equation (4)
18y - 8y = 51.60 - 33.60
10y = 18
y = 18/10 = 1.80


Substituting this value of 'y' in equation (1) we have
3x + 4*1.80 = 16.80
3x + 7.20 = 16.80
3x = 16.80 - 7.20 = 9.60
x = 9.60/3 = 3.20


Thus, each burger costs $3.20 and each fry costs $1.80.