Revenue in Australia is , so marginal revenue is . Revenue in NZ is , so marginal revenue is .
, and we need to find the marginal cost for each good. That can be found by taking the partial derivative with respect to x, then the partial with respect to y.
Now you can set marginal revenue equal to marginal cost in each region.
So and . Solving each equation means x=35 and y=42.5 (the latter should probably be rounded down to 42).
Does that help?