Can someone please help me with this question. I need to know if cutting price by 10%, sales increase to how many pizzas? And total revenue will

Can someone please help me with this question. I need to know if cutting price by 10%, sales increase to how many pizzas? And total revenue will increase to how much? Please help.

A local pizzeria sells five hunderd large pepperoni pizzas per week at a price of twenty dollars each. The price elasticity of demand for his pizza is -4. I need to know two things.

Thank you