Sita and Geeta start at the same time to ride from place A to place B, which is 90 km away from A. Sita travels 3 km per hours slower than Geeta. Geeta reaches place B and at once turn back meeting Sita 15 km from B. Sita's speed (in km/h) is:

Distance between A and B is 90 km 

Speed of Seeta = Speed of Geeta - 3 

According to conditions given in the Question : 

Distance covered by Seeta = 75 km

Distance covered by Geeta = 105 km 

Ratio of distance covered by Seeta : Geeta = 75 : 105 

i.e, 5 : 7

We know, the ratio of Distance = ratio of Speed 

Lets their speed be 5x and 7x 

Difference between their speed is 7x - 5x = 2x = 3 km/hr (given) 

1x = 1.5 km/hr

Speed of seeta = 5x 

i.e; $$5\times\ 1.5=7.5\ \frac{km}{hr}$$

Hence, Option D is correct.