From Econ-251 that need to calculate the change producers surplus while the answer is A and I need the process for it. I know the formula is like this Change PS= -(100 + 1/2*1*5) = -102.5 million That where does the 100 came from or which triangle Should I calculate to come up with answer. I need the process

Price |dollars per pack) D - tox on buyers e 1 L ~ L 0 90 95 100 105 110 Quantity [millions of packs per year) 16. The figure above illustrates demand and supply in the market for milk. If the government decides to impose the sales tax on buyers, then the change in producer surplus is a) -$102.5 million b) -$100 million ) -$205 million d) -$7.5 million