Here are the equations that are represented by the scenarios:
4x + 2y = $14 (Joe)
3x + y = $9 (Becca) or y = 9 - 3x
To find the cost of each burger and fry you will solve the second equation for y and substitute it in for the y in the first equation. This will put everything in terms of x, the price of a fry.
4x + 2(9 - 3x) = $14
4x + 18 - 6x = 14
-2x +18 = 14
-18 -18
-2x = -4
-2 -2
x = 2
Fry cost $2, and burgers cost (9 - 3 x 2) or $3.
