How to calculate price depending the room type and check in-out dates

A costumer needs to rent a room

i need a easy way to calculate the total price
depending the check in, check out dates and the type of the room

two rooms, the one cheap the other one expensive
the price changes every month (only 4 summer months)

Room 1
price 10 euro per day (june)
price 20 euro per day (july)
price 30 euro per day (August)
price 15 euro per day (September)

Room 2
price 20 euro per day (june)
price 30 euro per day (july)
price 50 euro per day (August)
price 25 euro per day (September)

<select name="room" id="room" >
<option value="">Select Room</option>
<option>Room 1</option>
<option>Room 2</option>
</select>                   

<input type="text" id="checkin" name="checkin" >

<input type="text"  id="checkout" name="checkout" >

<input type="number"  id="Totalamount" name="Totalamount">
             

How it is possible to calculate it?

Using Java, php, SQL ??????

Thanks in advance