XCTAssertEqual failed: 
("h(t) = -16.0t^2 + 17.880t + 51.0") is not equal to 
("h(t) = -16.0t^2 + 17.88t + 51.0") 
XCTAssertEqual failed: ("x(t) = 83.070t") is not equal to 
                       ("x(t) = 83.07t") 

Yeah, really. They're not the same.

EVERYTHING, including values in the equations appearing as coefficients, must be rounded to THREE decimal places.

But because there is no proper order in XCTAssertions, it could be your answer is right and the expected one is wrong, please elaborate.

what's the point of this AI slop reply

Nice. Thank you for your hint! Didnt know that :)

Print the input, read the error message, it'll become obvious what to do to fix your code.