A particle starts from rest on a straight path, Its acceleration is linearly varying with time, such that velocity of the particle at t=2 sec and t=4 sec is `6ms^(-1)` respectively. Find acceleration of the particle at t=i sec.
A. `1.5ms^(-2)`
B. `2 ms^(-2)`
C. `3 ms^(-2)`
D. `2.5ms^(-2)`