Let f be a function of two variables that has continuous partial derivatives and consider the points A$(3,3),$B$(7,3),$C$(3,9),$ and D$(11,18).$ The directional derivative of

f at A in the direction of the vector $()/($bar$)($AB$)$ is $7$ and the directional derivative at A in the direction of $()/($bar$)($AC$)$ is $1.$ Find the directional derivative of f at A in the direction of the

vector $()/($bar$)($AD$).($Round your answer to two decimal places.$)$