Answer:
62 miles
Explanation:
The formula for average is given as
Sum of values / Number of values
Let x = miles on the last day
Hence
48 + 51 + 59 + x/4 = 55
Cross Multiply
= 158 + x = 220
x = 220 - 158
x = 62
Therefore, he needs to bike 62 miles on the last day so that his average (mean) is 55 miles per day.