Another online shop sells face masks worth Php 5.50 per piece if you will only purchase 100 masks or below, plus a shipping fee of Php 20.00. If you buy more than 100 masks, the shipping fee is waived and the price of the face masks become Php 4.50 per piece. What function F represents the amount you will pay to the delivery rider if you purchase x number of face masks from this other shop?​