Answer:
Step-by-step explanation:
a1 = 0
an = a1 + (n -1)*d = 3n - 3
(n - 1)*d = 3(n-1)
From which d = 3
Now for the sum
Sum = (a1 + an)*n/2
Sum = (an * n)/2
Sum = 3(n - 1) * n / 2
Sum = (3n - 3)*n/2
Sum = (3n^2 - 3n)/2
