Medium is
a. the materials used by an artist.
b. the aesthetic balance an artist achieves in his/her work of art.
c. the relation of one part to another, or of parts to the whole.
d. a reproduction of people, places, or things.

Option A i.e The materials used by an artist is the correct answer.

With regard to the art, the medium simply refers to the material used by an artist to create a piece of artwork. Marble, Painted steel plates, proclean etc are some of the mediums used by artists to create the beautiful pieces of art work. For example, Michelangelo used the medium of marble to create "David"(1501-1504).

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form

the answer is 12 as i may remember

: )