Novice Problem for Final Velocity

[PhysicsAdvice]

1. A lab was performed where students roller an initially stationary cart down a ramp 1.84m long. It took 1.15s to roll off the end of the ramp. What is the final velocity of the cart?
vi=0m/s, D=1.84m, t=1.15s vf=?



2. Vav=d/t, Vav= (vi+vf)/2



3. Vav= 1.84m/1.15s=1.6m/s 2Vav-vi=vf, 2(1.6m/s)-0=vf, therefore vf= 3.2m/s

Sorry for wasting everyone's time with this novice problem, however, if this was firstly correct, and secondly the easiest way of finding final velocity. My textbook states a different answer and I was wondering if I made an error or if it was mistaken. Thanks.

 

[iRaid]

Simple:
$$V_{f}^2 = V_{i}^2 + 2 a \Delta x$$

 

[PhysicsAdvice]

so to find acceleration would I need to find delta velocity and then just use a=v/t?