Answer:
(a)The missing measurements are 9 feet and
.
(b)Therefore, the length of the fence is 
Step-by-step explanation:
The diagram of the yard is attached below.
(a)I have labeled the missing dimensions of the yard as x and y.
Therefore:

Similarly:

The missing measurements are 9 feet and
.
(b)Length of the Fence
The fence is rectangular shaped with:
Length = 
Width = 
Perimeter of a Rectangle = 2(L+W)
Therefore, the length of the fence

Pythagorean Theorem is for right triangles
right triangles have a 90 degree angle in them
D is a right triangle
The mean is calculated by adding up all of the given numbers and dividing by the number of numbers.
Lets, for ease of understanding, say that the first three number were 64...
Mean=(64+64+64)/3=192/3=64
Now, lets solve for the mean where 'x' is the unknown fourth number and 128 is the mean. (since, the answer said that when the fourth number was added the mean, 64, was doubled '64*2=128')
128=(64+64+64+x)/4
128=(192+x)/4
Multiply both sides by 4
512=192+x
subtract 192 from both sides
320=x
The missing number is 320..
Now lets double check our work.
Mean=(64+64+64+320)/4=512/4=128
Answer=320
To find the probability of not having twins, we can subtract the probability of having twins from 1. This is because probabilities always add up to 1.
1 - 0.015 = 0.985
The probability of not having twins is 0.985.
Hope this helps!! :)