This is the sum of an arithmetic series
n ( a1 + a1 + (n -1) d) / 2 > 300
a1 = 6 = the first term
n = the number of days
d = the common difference = 8
So we have
n ( 6 + 6 + (n-1) * 8 ) / 2 > 300
n ( 12 + 8n - 8) > 600
n ( 4 + 8n) > 600
4n + 8n^2 > 600 divide through by 4
2n^2 + n > 150
2n^2 + n - 150 > 0
Solve this
2n^2 + n -150 = 0
Using the Quadratic Formula
n = -1 + sqrt ( 1^2 - 4 (2) (-150) ) -1 + sqrt ( 1201)
_________________________ = _______________ ≈ 8.41
2 * 2 4
He will run out sometime during the 9th day
