The simple rule of thumb applied to differentiation can be used in this example - 'Multiply each term by its power then reduce the power by one'. Doing this 5x^2 becomes 25x^(2-1)=10x. Repeating for 11x gives 111x^(1-1)=11x^0=11x as anything to the power of 0 = 1. Finally 5 disappears when differentiated with respect to x as it is not a function of x. Ie. it has no x terms in it.