Length = 99 because...
since you multiply to get the area, in order to find the missing term of an area (in this case its length), you do the opposite of what you started with...so if you multiplied to get the area, you need to divide to get the missing side...
so 8811 divided by 89 = 99
99 x 89 = 8811
See attachment file below.
It can be inferred that the siblings of the autistic children in the study do not have autism.