What statement did Niels Bohr make about atoms?

Can someone explain to me how to do this problem ?

Consider the following position function. find (a) the velocity and the speed of the object and (b) the acceleration of the object. bold r left parenthesis t right parenthesisr(t)equals=left angle 6 t superscript 4 baseline comma 2 t cubed right angle6t4,2t3 for tgreater than or equals≥0

Which of the following is the best name for mgcl2