Answer:
700 units 
Step-by-step explanation:
Calculation for the what the size of the order will be.
Using this formula 
Unit to sell= Total additional fixed costs + desired profit / Contribution margin per unit=
Let plug in the formula 
Units to sell=$550 + $850 / (8-6) 
Units to sell= $1,400/2
Units to sell=700 units
Therefore the size of the order will be 700 units