The average of five consecutive natural number is 15. What is the sum of the first and last numbers

Correct option is B

Let 5 consecutive natural numbers are:
x, x+1, x+2, x+3, x+4
sum of 5 consecutive natural numbers = 75
or, x + x+1+x+2+x+3+x+4 = 75
or, 5x + 10 = 75
or, 5x = 75-10
or, x = 65/5
x = 13
so, the 5 consecutive numbers are:
13, 14, 15, 16, 17
Hence required sum = 13 + 17 = 30