Extra Guests

Chef planned a party, and expected $X$ people to be there. However, more people than expected turned up, so that finally there were $Y$ people at the party! Chef now has to ensure that there's enough food for everyone. Chef has already ordered $X$ plates of food, each costing $100$ rupees. For each extra guest at the party, Chef needs to order one plate of food — which now costs $150$ rupe