Answer:
2436
Step-by-step explanation:
The sum of n terms of an arithmetic series is given by the formula ...
Sn = (n/2)(2a +d(n -1))
where a is the first term, and d is the common difference.
__
This series has ...
a = 46
d = 53 -46 = 7
n = 21
So, the desired sum is ...
S21 = (21/2)(2(46) +7(20)) = 2436
The sum of the first 21 terms is 2436.
