A train overtakes two persons walking along a railway track. The first one walks at 12.6 km/hr.

Let the speed of the train be $x$ km/hr.

Since both persons are walking in the same direction as the train:

Relative speed with first person = $(x - 12.6)$ km/hr

Relative speed with second person = $(x - 30.6)$ km/hr

Length of the train remains same in both cases.

So,

$(x - 12.6)\times 19.8 = (x - 30.6)\times 25.8$

Expanding,

$19.8x - 249.48 = 25.8x - 789.48$

$540 = 6x$

$x = 90$

Therefore, the speed of the train is:

$\boxed{90 \text{ km/hr}}$

Correct option: 90 km/hr