Seema has joined a new Company after the completion of her B.Tech from a reputed engineering college in Chennai. She saves 10% of her income in each of the first three months of her service and for every subsequent month, her savings are Rs. 50 more than the savings of the immediate previous month. If her joining income was Rs. 3000, her total savings from the start of the service will be Rs. 11400 in:

Seema saved Rs. 900 in the first 3 months. She must saved Rs. (11400 - 900) = Rs. 10500 in the subsequent months.

The sequence will be of the form: 350 + 400 +........... $$n$$ terms = 10500

=> $$\frac{n}{2}$$ [2*350 + ($$n$$-1)*50] = 10500

=> $$\frac{n}{2}$$ [70 + ($$n$$-1)5] = 1050

=> $$n^{2}$$ + 13$$n$$ = 420

Solving, we get $$n$$ = 15

The savings of Rs. 10500 is done in 15 months. Seema saved Rs. 11400 in 15+3 = 18 months.

Hence, option C is the correct answer.