Step-by-step explanation:
3.
the net of a cylinder looks like a rectangle with two circles attached at opposite ends. we also define a base radius for the cylinder as the radius of the base, and the height of the cylinder as the distance between the bases.
in other words, imagine you cut open a soda can (and leave the top and bottom just a little bit attached - don't cut them off completely).
the mantle turns into a rectangle. and the base and top are two circles. the length of the rectangle is the circumference of one of the circles (2×pi×r), and the width of the rectangle is the height of the original can.
4.
remember what you did when calculating the size of the area of a square ? or a rectangle ?
in each case it is in principle length×width.
and we expressed an area not in units of e.g. cm but in cm², because we simply said how many little squares of 1 unit side length fit into the area.
now, for the volume, we apply the same principle and simply add a third dimension.
we express a volume not in cm² squares but in cm³ cubes, saying how many such little cubes fit inside.
a cube with 5 cm side length has therefore a volume of
5×5×5 = 5³ = 125 cm³ (= 125 little cubes of 1cm side length).
5.
this is simply a box, a 3-dimensional rectangle.
similar to 4. fit the volume we just multiply now so 3 dimensions :
6×7×9 = 378 cm³ (= 378 little cubes of 1cm side length).
