Final answer:
The mass used with an 8 to 1 grid cannot be determined from the given information.
Step-by-step explanation:
The question is asking how much mass would be used if an 8 to 1 grid is used instead of a non-grid exposure. To find the mass, we need to consider the exposure factors given, which are KVP, MAS, and the fact that 35% of the x-rays are absorbed in 20.0 kg of tissue with an exposure time of 0.250 s. The mass used with an 8 to 1 grid cannot be determined from the given information.
However, the given information does not provide a direct equation or relationship to calculate the mass. Therefore, it is not possible to determine the exact amount of mass to be used with an 8 to 1 grid without additional information.