If a - 4 = 4 (2- a), then what is the value of a?

If 2x + 3y -31, y – z - 4 and x + 2z – 11, then what is the value of x + y + z ?

If f (x+(y/8), x-(y/8)) = xy, then f (m, n) + f (n, m) = 0

If  x *y=x2 + y2 – xy, then the value of 9*11 is:

[{√196-√64}*-2.5]=(?)

If 3x – 4y + z = 7; 2x – z + 3y = 19; x + 2y + 2z = 24, then what is the value of z ?

The number of positive integers n in the range 12  ? n? 40 such that the product (n – 1) (n –2)…3.2.1 is not divisible by n is 

If 4x + 5y = 83 and 3x/2y = 21/22 how much is y – x

Solve for real x: 6x² + 5x - 6 ≥ 0