Answer:
19404
Step-by-step explanation:
sum of arithmetic series is
Sn = n/2 (2a + (n-1)d)
or
Sn = n/2 (a + an)
a = 1st unit
an = last unit
d = difference
8-3 or 13-8 so d = 5
then first step is to find the value of n
an = a + (n-1)d
438 = 3 + (n-1)5
438 - 3 = 5n - 5
435 = 5n - 5
435 + 5 = 5n
440 = 5n
n = 440/5
n = 88
then we can find the sum
Sn = 88/2 (3 + 438)
S88 = 19404
