23) (4/3 t³ + ...)² = ... + 8/3 t⁵h + ...

The expression is of the form (a+b)², where a=4/3 t³ and 2ab = 8/3 t⁵h. Thus, b=h. (4/3 t³ + h)² = (4/3 t³)² + 2(4/3 t³)(h) + h² = 16/9 t⁶ + 8/3 t³h + h². The missing terms are 16/9 t⁶ and h².