A student starts form his house to his school far away by $$1\frac{3}{4}$$ km, reached 6 minutes late travelling with a speed of $$2\frac{1}{2}$$ kmph. The speed by which he has to increase so as to reach the school 6 min early (in kmph) is

A

$$3\frac{1}{2}$$

B

1

C

$$\frac{1}{2}$$

D

$$3\frac{1}{4}$$