How does vacuum reduce thermal energy transfer

Less air pressure.

Explanation:

Thermal energy travels in many different ways and one of those ways is through the air so if there's less air, it would reduce thermal energy transfer.

option number c is the right answer.

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