If x + y = 7 and 2x − y = 8, then y − x is equal to

If x² + 1/x² = 51, then (x − 1/x) is equal to

If y/x = 2 − x/y, then the value of (x³ + xy²)/(x³ + y³) is equal to

If a/h + y/b = 1 and b/y + z/c = 1, then h/a + c/z will be equal to -

If 1² + 2² + 3² + ... + 10² = 385, then 3² + 6² + 9² + ... + 30² is equal to:

If x + (1/y) = 1 and y + (1/z) = 1, then the value of z + (1/x) is