Your own answer is absolutely correct, it’s really $85 per week. To get the right answer you need to know that since supply is elastic then the producer’s price will be $1 fixed. It means that only the consumer must pay the tax so his price rises to $1.10. Now let’s take into account the demand elasticity which is -1.5. If we increase price by 10% then we’ll see 15% decrease in demand (850 units). All there’s left to do is just apply 10% to the sales price and get the answer: $85.