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Yup you go it. Although the cat and turtle height is undefined. They can be 100 cm and 80 cm and the Table will still be 150 cm!

I think cat and turtle height depend on each other: the cat needs to be 20 cm taller than the turtle. Apart from that, their absolute heights are undefined, right?

Yup that's right. There are 2 equations and 3 unknowns so this is expected.