Question 363769
The sequence is an arithmetic sequence with a1 = 14, d = 2, and n = 25.  Then a25 = 14 + (25-1)*2 = 14+24*2 = 14+48 = 62.  There are 62 marchers in the last row.  There are {{{S = 25(14+62)/2 = 950}}} marchers all in all.