How do I find the acceleration of gravity

[Vodkacannon]

I need to find the acceleration of gravity in my area (I live 287 meters above sea level.)

I know that y = 0.5*g*t², y=(v₂²-v₁²)/2*g, f_g=m*g, and F= G*m₁*m₂/d^2

I placed a ramp at an arbitrary angle. I found the height of the ramp, the angle of the ramp, and the length of the ramp.
I placed a cart on the ramp and let it run down to the end of the ramp, timing the whole trip.
I've got all this data and I'm not sure how I would calculate g, for it is a vertical force and my ramp is somewhere in-between 90 and 45 degrees.
(I have messed around with trig. but got no where).

You see I haven't given you all of the data, I'm not looking for the exact answer I just need a general statement on how to find g in this situation.

My teacher gave me a hint, he said to "extrapolate."

 

[CWatters]

The acceleration you measured down the slope is due to that component of gravity that acts down the slope. Draw the diagram and show us what trig you used and perhaps we can see the error.