Final answer:
Mr. Jackson only needs to fill the pyramid and pour it into the prism once to completely fill the prism with water.
Step-by-step explanation:
To determine the number of times Mr. Jackson must fill the pyramid with water and pour it into the prism in order to completely fill the prism with water, we need to consider the volume of each shape. Since the bases are congruent and the heights are equal, the volume of the pyramid is equal to the volume of the prism. Therefore, Mr. Jackson needs to fill the pyramid and pour it into the prism once to completely fill the prism with water.