First we set the chicken dish as the variable x and the beef dish as the variable y.
x + y = 250
5x + 7y = 1500
We then solve for x on one of the equations.
x = 250 - y
Then we plug this into the second equation.
5(250 - y) + 7y = 1500
1250 -5y + 7y = 1500
2y = 250
y = 125
Karina served 125 beef dishes.
We then plug this value into x + y = 250 to find x.
x + 125 = 250
x = 125
Karina served 125 chicken dishes.
