Try this:
1. sum of numbers is x+y=67, the difference between them is x-y=11
2. it is possible to make up and resolve the system:
f(x)=2x^3+2x^2-4x
The zeros of polynomial functions
2x^3 + 2x^2 - 4x = 0
2x(x^2 + x - 2) = 0
2x(x - 1)(x + 2) = 0
2x = 0; x = 0
x - 1 = 0; x = 1
x + 2 = 0; x = -2
Answer
x = -2 , 0 , 1
After manipulating above equation we get, 2x^2 - 7x - 8= 0. Discriminant= b^2 - 4ac = (-7)^2 - 4(2)(-8) = 113>0. So there are 2 real roots :)