k means 1000 (its not a variable)
let target for jan=t.
then for feb = t+x
for nth month = t+(n-1)x (n goes from 1 to 12)
to find t+2x
a) t+11x=310k
insufficient. 2 variables, 1 equation.
b) t+8x = 30k+t+5x =>x=10k
we don't know t, insufficient.
a&b) x=10k, t+11xk=310k =>t=310-110=200k
thus for march t+2x = 220k
IMO C

IMO C

1.target for dec next yr is 310000

we do not know the difference by which revenue for each successive month increases. So Insufficient.

2.target for sept next year is 30000 > than rev for june next year.

let difference by which revenue for each successive month increases be "x" and revenue in June be "y"

so, revenues in July, Aug ,and Sept will be y+x, y+2x and y+3x respectively.

Given that, target for sept next year - rev for june next year = 30000 => (y+3x) - (y)= 30000 => x = 10000

Because we have no info about revenue in any of the months we cannot calculate the target for march next year.

So Insufficient.

Combining 1 and 2
we know the December revenues and the difference between successive months' revenues, we can calculate the target for march next year.(No need to calculate).
So, Sufficient.