Children can go to school either by van or by minibus. A van can take 6 kids and produces 7 units of pollution. A minibus can take 10 kids and produced 10 units of pollution. There are at least 150 kids than need to go to school and at most 10 minibuses can be used. In addition, the number of vans used must exceed the number of minibuses. How many of each should be used to minimize the total amount of pollution produced?