Determine the Constant of Variation for the Stated Condition $12.5$ Gallons of Water

Multiple Choice

Determine the constant of variation for the stated condition.
-The amount of water used to take a shower is directly proportional to the amount of time that the shower is in use. A shower lasting 25 minutes requires $12.5$ gallons of water. Find the amount of water used in a shower lasting 10 minutes.

A) 5 gallons
B) $31.25$ gallons
C) 20 gallons
D) $1.25$ gallons