Flexible Budgets and Variances

The question goes like this..

You are provided a cost card
The Fixed Overheard per unit = $2

The Fixed overhead charged to each unit of the product is based on a monthly production level for product A of 500 units

Last period actual level of activity was 750 units and the fixed overhead was $1700

The question is to find the total fixed expenditure variance.

If anyone knows the answer, please post the rationale too.

Thanks