Based on the given problem above, Mr. and Mrs. Fisk have 8 children and with each child they have, has also 8 children. So to get the number of their grandchildren, we will multiply the number of Mr. and Mrs. Fisk have to the number of children that each child has.
1 child of Mr. and Mrs. Fisk = 8 children
8 x 8 so the result would be 64. Mr. and Mrs. Fisk has a total of 64 grandchildren. I hope this answer helps.