Sea level is taken to be 0 feet. If we place this on the number line, values of elevation above sea level would be positive and would be on the right hand side of zero on the number line. Also, values of elevation below sea level would be negative and would be on the left hand side of zero on the number line.
Given that the scuba diver is at an elevation of 53 feet below sea level, the value is - 53 ft
Given that the hiker is at an elevation of 228 feet above sea level, the value is 228 ft.
Therefore, the difference in elevation between the scuba diver and the hiker, in feet would be
228 - (- 53)
= 228 - - 53
= 228 + 53
= 281 feet
Therefore, the difference in elevation between the scuba diver and the hiker, in feet is 281 feet