Answer :

just subtract them
4-4=0
9-3=6

the distance is 6 since the x part stayed on the sam line
[tex]d=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}\\\\ d=\sqrt{(4-4)^2+(9-3)^2}\\ d=\sqrt{0^2+6^2}\\ d=\sqrt{6^2}\\ d=6[/tex]