Question

koe eska answer bata dou​

Answer 1

a= 24

d= 21-24 = -3

Sum = 78

We have to find n

Sum= n/2 ( 2a + (n-1) d )

78 = n/2 ( 48 + ( n-1 ) -3 )

156 = n ( 48 -3n +3 )

156 = 51n - 3n^2

3n^2 - 51n + 156

After solving this you will get answer

n = 4 and 13

Hope it helps.

Please mark it as brainliest answer.