Answer:
Number - 47
Step-by-step explanation:
difference means subtract
Number - 47
y = -1/2x + 5 should be your equation because it is 5 ft above sea level and its eroding, or going down, 1 ft per 20 years. So every year, the sand dune erodes 1/20 ft more.
Hope this helps!
Sick my dock is the answer