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

• A

  20

• B

  30

• C

  50

• D

  80