Answer:
x = 10
Step-by-step explanation:
She must have multiplied it by 5.
That would've given her:
x - y = 15
2.5x + y = 25
Now we can add them and the y-terms will eliminate each other. Because one is -y, and the other is positive y. -y + y = 0.
F(x) = x^2 + 24x + 138
f(x) = x^2 + 24x + (24/2)^2 + 138 - (24/2)^2
f(x) = (x+12)^2 - 6
