determine the sum of the first fourteen terms of arithmetic series

A formula that calculates the sum is:  Sum  =  n(f + l) / 2

where  n  is the number of terms (if you want the sum of 14 terms, n = 14),

f  is the value of the first term, and

l  is the value of the last term (if you want the sum of 14 terms, l is the value of the 14th term.