Output of Good-X decreases by 400 units and output of Good-Y increases by 400 units, and some resources are shifted from the production of X to the production of Y, the marginal opportunity cost is
1.0
Marginal opportunity cost is the cost when a unit more of a good is produced by withdrawing some resources from the production of other good. When resources are shifted from Good-X to Good-Y, the output of Good-X decreases by 400 units and output of Good-Y by 400 units, implying an overall change of 1.0 (400/400).