Constant Acceleration Questions

A particle moves in a straight line with a constant acceleration. It changes its velocity from $10{\text{ms}}^{-1}$ to $20{\text{ms}}^{-1}$ while passing through a distance of $135\text{m}$ in $t$ seconds. What is the value of $t$?

A particle starts its motion from rest under the action of a constant force. If the distance covered in the first $10$ seconds is $S_1$ and that covered in the first $20$ seconds is $S_2$, then: