I've got the same position and time as you, but it seems I am still having trouble. In order to eliminate the possibility of accidently entering in a 10 digit number incorrectly, I've deducted a nice little formula that should just spit the answer right out, but it doesn't seem to spit out a correct one.

First of all our relevant green car positions and times in km and hours this time:

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Next is our nice equation. The following should be true under three conditions:

1) our initial position and time are both 0

2) acceleration is constant

3) beyond our initial position and time, we have two more pairs of position and time values

We can next set up a nearly identical equation for our second pair of position and time

Now we can set these two equations equal to eachother and solve for a, the only remaining variable.

This seems real nice. It seems like it is impossible to get an incorrect answer now, but when I plug in my two pairs of values, I get

I am assuming that since every value entered into the equation was in km and hours, that this number is in km / h<sup>2</sup>. Using the conversion method Jane mentioned above, I should be dividing this number by 12960. This gives me the final answer of:

83.92978815 m / s<sup>2</sup>

however it seems this answer is still incorrect.