Asand dune stands 5 feet above sea level. the hill is eroding at a rate of 1 foot per 20 years. let y represent the height of the sand dune after x years. which equation represents the situation?

The situation will be represented by linear equation, this is given by:
y=ax+b
where:
a=slope=rate
b=y-intercept
from our situation:

a=-1/20
b=5 ft
thus the equation modeling the situation will be:
y=-1/20x+5

y=-1/20x+5