Of the three primary forms of subaerial volcanoes, are large cone-shaped mountains that consist of alternating layers of tephra and solidified lava.

Strato-volcano

Explanation:

Strato-volcanoes are usually characterized by the presence of steep-sided slopes, with distinct craters, and are frequently erupted and conical in appearance. This type of volcano is generally felsic in nature. Due to the presence of high silica content, the magma being highly viscous, moves at a relatively slower rate. These are highly explosive and produce a large number of pyroclastic materials, lava flow, volcanic ashes, and gases.

They are also commonly considered as the composite volcano, and are comprised of alternating tephra and solidified lava layers.

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