Update arrays_and_math.adoc added code sample needed to generate the file.txt...

Update arrays_and_math.adoc added code sample needed to generate the file.txt file with data for processing in the activity

Activities/arrays_and_math.adoc

 ===== Activity: Array Indexing and Math (1340-1410) Review to 1440
-* Copy C:\file.txt to your Desktop
-* Write a PowerShell scrip to do the following:
+* Create  file.txt on your desktop by running the following PS script:
+[source,]
+----
+
+#This code will generate a file with the data for the exercise
+[int]$i = $Null
+do  
+{
+$i ++
+Add-Content C:\Users\$env:UserName\Desktop\file.txt $i
+}
+while ($i -lt 1000)
+----
+
+* Write a PowerShell script to do the following:
 ** Read file.txt on your desktop
 ** Extract the 135th(x), the 227th(y), the 578th(z) and the 892nd(n) numbers
 ** Add x and y and output the result