Final answer:
Katherine Johnson was asked to check the math of the men at NASA because of her skills and contributions as a mathematician.
Step-by-step explanation:
Katherine Johnson was asked by Mr. Harrison to check the math of the men at the Space Task Group at NASA because she was a skilled mathematician who made significant contributions to NASA's success.
She was known for her calculations of orbital mechanics and for calculating the trajectory for the first moon landing. Her expertise and dedication made her a valuable asset to the team.