The statement tells us that the market share has increased from 3% to 9% and more mobiles have been sold overall. This indicates that the total number of mobiles sold in 2019 is more than in 2018, which supports Inference I.
Inference II mentions that the sales of mobile company X have tripled, but the statement does not specify the exact increase in the number of units sold. Therefore, we cannot conclude that the sales have tripled from the given data. Hence, inference II does not follow.
The correct answer is (c) Only inference I follows.