I want to directly call the result value by arithmetic operation on two state values

I want to display (salePrice + manualSettlementAmount), (salePrice -manualSettlementAmount), values ​​according to the operation of sale state ‘+’, ‘-‘. And these result values ​​are put in settlementAmount.

And the arithmetic operation values ​​are calculated in onBlurSettlementAmount.

  const [form, setForm] = useState({
    sign: "+",
    salePrice: "",
    manualSettlementAmount: "",
    settlementAmount: 0,
  })

  const onChangeSign = (event: React.ChangeEvent<HTMLSelectElement>) => {
    setForm({...form, sign: event.target.value}); 
  } 

  const onChangeSalePrice = (event: React.ChangeEvent<HTMLInputElement> | any) => {
  setForm({...form, salePrice: event.target.value});
  }

  const onChangeManualSettlementAmount = (event: React.ChangeEvent<HTMLInputElement> | any) => {
    setForm({...form, manualSettlementAmount: event.target.value });

  }

  const onBlurSettlementAmount = (event: React.ChangeEvent<HTMLInputElement> | any) => {

    if (form.sign == '+') {
      setForm({ ...form, settlementAmount: (Number(form.salePrice) + Number(form.manualSettlementAmount ))})
    } 
  
    if (form.sign == '-') {
      setForm({ ...form, settlementAmount: (Number(form.salePrice) - Number(form.manualSettlementAmount ))})
    }
    
  }

return (
 <>
       <select value={form.sign} onChange={onChangeSign}>
                  <option label="+" value={"+"}>+</option>
                  <option label="-" value={"-"}>-</option>
       </select>

      <input type="text" value={form.manualSettlementAmount} onChange={onChangeManualSettlementAmount} />
      
      <input type="text" value={form.salePrice} onChange={onChangeSalePrice} />      

      <input type="number" disabled={true} value={form.settlementAmount} onBlur={onBlurSettlementAmount} />
 </>
)

However, the value of settlementAmount in input continues to appear as an initial value of 0, and the arithmetic operation value is not displayed. I don’t know why.

After inputting both sign and salePrice, whenever I input the manualSettlementAmount value, I want the settlementAmount value to be displayed as well.. How should I handle it?

Is it not possible to do arithmetic operations in onBlur?