Algebra word problem

Question

The average height of mountain A is 14,230 ft, and its average height is 8890 ft less then the sum of the average heights of mountain B and C. The average height of mountain C is 280 ft less than four-fifths of the average height of mountain B. Find the average height of mountain C.

Answer 1

14230<b+c=b+4b/5 -280

c=4b/5 - 280

4b/5 =c+280

b =5c/4 +350

14230 < (5c/4 +350) + c= 9c/4+ 350

13880 < 9c/4

4(13880)/9 < c

c > 6168 8/9 feet

also

c = 4b/5 -280 feet