The formula for volume is V = lwh
This means that the volume is equal to the length times the width times the height.
Multiply the three numbers for your answer.
Length = 4, width = 3, height = 9
lwh = 4cm X 3cm X 9cm = 12cm^2 X 9cm = 108cm^3
And there you have it! Your final answer is 108 cm^3 OR 108 cubic centimeters!
I do not mean to scare you, but this is the most basic volume formula! As you encounter different 3D shapes, the formulas will change!
You are going to want to practice with more of this type of problem before you move on to other shapes!