Answer:
g(x) = 0.8x gal/dollar
Step-by-step explanation:
This is a direct relation, each gallon costs 1.25, 20 gal. costs 25.00, etc.
so
f(x) = 1.25x where x = number of gal. f(x) is the cost
The inverse relation is the reciprocal,
for each $1.00, we can buy 1/1.25 = 0.8 gal.
or
g(x) = 0.8x where x = amount, g(x) is number of gallons