financial planning 既一條題目,,幫幫手,,OK?(15)

題目如下::

Sarah's comprehensive major medical health insurance plan at work has a
deductible of $1500.The policy pays 85% of any amount above the deductible.
While on hiking trip, she contracted a rare bacterial disease. Her medical costs for treatment,
including medicines, tests, an a six-day hospital stay, tataled
$ 81893.
How much Sarah need to pay?
{1500+(81893-1500)X15%}
How much Sarah can claim from insurance company?
{(81893-1500)X85%}

我有answer架啦
不過都唔係好明個$1500點解
又話係扣除,但係都好似要俾...
仲有>$1500,係邊個只需俾85%?

可以用中文解D formula俾我知嗎??
幫幫手,,OK?