If a - b = 4 and ab = 12, what is the value of a² + b²?

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

If x³ = (9³ × 6³) / 8, x > 0, then what is the value of x?

If 2ˣ × 3ʸ = 12 and 2ʸ × 3ˣ = 18, then the value of x + y is :

If a, b, c, d, e and f satisfy 2a = 3b = 6c = 9d = 12e = 18f, then what is the value of (a + b)/(c + d + e + f)?

If x + (1/x) = 3, then the value of x³ + (1/x³) is :