Find the x co-ordinate of stationary point of the graph y=5x^3 +3x

When you differentiate the function that gives the gradient. Therefore differentiate to get dy/dx= 15x^2 + 3. Make this equal to 0 to get 15x^2 + 3=0 and rearrange to get the value of x as required so 15x^2= -3 and so on