,

By the Sum Rule, the derivative of with respect to is .

Evaluate .

Since is constant with respect to , the derivative of with respect to is .

Differentiate using the Power Rule which states that is where .

Multiply by .

Evaluate .

Since is constant with respect to , the derivative of with respect to is .

Differentiate using the Power Rule which states that is where .

Multiply by .

Replace the variable with in the expression.

Multiply by .

Add and .

Evaluate the Derivative at x=7 f(x)=8x^2+11x , x=7