Calculate for the first term of the series
an = (a1) x (n - 1) x d
Using the value of a7 = 46 and the rate of increase
46 = (a1) x (7 -1) x 7
The value of a1 is 4.
Solving for the sum of 19 terms,
Sn = (n/2) x (2a1 + (n - 1) x d)
Substituting,
Sn = (19/2) x ((2)(4) + 18 x 7)
The sum of the first 19 terms is 1,273. Therefore, the answer is letter B.
