Subject :NSO Class : Class 9

** A particle is moving in a straight line with initial velocity
u and uniform acceleration f. If the sum of the distances travelled in
t^{th} and (t +
1)^{th} seconds is 100 cm, then its
velocity after t seconds in cm/s is **

(A) 20

(B) 30

(C) 50

(D) 80.

explanation please