What is the sum of the arithmetic series below?

The question is to find the sum of the 15thb first term ( i goes from 1 to 15)
for i =1, the first term is 4
for I=15, the last term = 74
Sum of the terms of a AP = (first term + last term)(number of terms/2)
₁₅
∑F(n) = (4+74)(15/2) =585
i=₁

The amount used= 13.04- 1.9 = 11.14