Sum of first 12 terms of arithematic series is 186, 20th term is 186. Wat is sum of the first 40 terms

Answer 1

term(20)=186 ---> a+19d = 186
a = 186-19d

sum(12) = 6(2a + 11d) = 186
2a + 11d = 31
2(186-19d) + 11d = 31
-27d = -341
d = 341/27
a = 186-19(341/27) = -1457/27

sum(40) = 20(-1467/27+ 39(341/27) = -16041/27

better check my arithmetic, did not expect such weird numbers