A cross-section of an aeroplane wing has its upper boundary described by the curve y = a(x—3)², 0 ≤ x ≤ 3, where a is a positive constant. The height of the wing is y m at a distance of x m across the wing (relative to a reference point on the leading edge of the wing).

a. Show that the gradient of the curve is given by dy/dx = 3a(x —3)(x—1).
b. Hence, find the value of x at which this cross-section of the wing reaches its maximum height.