There were 340,000 cattle placed on feed
How many of the 340,000 cattle placed on feed were between 700 and 799 pounds?
Given the fraction of total cattle for 700 - 799 pounds is 2/5
Let x be the number of cattle between 700 - 799 pounds
We make a proportion using the fraction

Cross multiply it and solve for x
340000* 2 = 5x
680000 = 5x
Divide by 5 on both sides
So x= 136,000
There were 136,000 cattle between 700 and 799 pounds