In which one of the following intervals is the function $f(x) = \frac{x^3}{3}-\frac{7x^2}{2} + 6x + 5$ decreasing?

If the derivative of the function$f(x) =\frac{m}{x} +2nx + 1$ vanishes at x = 2, then what is the value of m + 8n ?

What is the area included in the first quadrant between the curves y = x and y = x³ ?

If xy = 4225 where x, y are natural numbers, then what is the minimum value of x + y ?