Answer:
144.
Step-by-step explanation:
Sum of n terms = (n/2)[a1 + l] where a1 = first and l = last term.
There are ( 1 + 23) / 2 = 12 terms in this series.
So the sum = (12/2) [ 1 + 23]
= 6 * 24
= 144.
276 is correct
I think y=x (1+3/5) is the right answer.
