Nice + coersion.

I concur, I was stuck on the nodegrade tests for a while before I read @docgunthrop's comment. (I probably should've realized that it was the obvious reason for 'nodegrade' to fail)

Javascipt (and maybe Dart)- It seems that either the tests are wrong or the example needs to be updated- should trailing 0s be included in formulas?
One of the test cases I failed in Javascript:

Expected: 'x(t) = 83.07t', instead got: 'x(t) = 83.070t'
Expected: 'h(t) = -16.0t^2 + 13.2t + 86.0', instead got: 'h(t) = -16.0t^2 + 13.200t + 86.0'

The instructions say:
EVERYTHING, including values in the equations appearing as coefficients, must be rounded to THREE decimal places. However, if the value is whole, only show one decimal place (for example => -16 becomes -16.0, not -16.000)

I believe this is an issue that only appears when you failed the "Input should not be modified" test. I solved that and it went away for me.