To start, the question is asking for surface area of a cylinder, meaning you will have to use this formula to find it: A=2πrh+2πr^2.
Since you already know that the diameter of the plastic cylinder is 4 marbles long, and each marble is 2 cm in diameter, you would multiply 4 and 2 to get that your diameter is 8 cm. However, since the surface area of a cylinder formula uses radius, you would simply divide 8 by 2 to get that the radius of the cylinder is 4 cm.
Now, since you already know that the height of the cylinder is equal to 10 marbles, multiply the amount of marbles by 2 to get that the height of the cylinder is 20 cm.
Now that you know the height and the diameter of the cylinder, plug the values into the formula: A=2π(4)(20)+2π(4)^2. Assuming that pi is 3.14, simplify the equation as according to PEMDAS and you get that the area of plastic needed to make one cylinder is 602.88 cm squared
