The gradient or the slope of a curve is defined as the change in the y direction over the change in the x direction (dy/dx). In order to calculate a formula for the gradient of a curve we must differentiate the curve's equation. Differentiating the equation we get 9x^2 + 7 which is an equation giving us the gradient of the curve at a given x value. In this question x=3 therefore the gradient of the curve is 88.