The normal price of each chair is

The percentage off the normal price is

The percentage of the present price of each chair will be

To calculate the present value of one chair, we will use the formula below

By substituting the values, we will have

Since Mr .Krabs bought 4 chairs, the amount he spent will be

By substituting the values, we will have

Therefore,
The amount Mr.Krabs spent is = $6.30