Tira obtains two fire insurance policies on her house. Each is an open policy with a pro rata clause. Tira's policy with Unity Insurance Company is for a maximum amount of $100,000. Her policy with Verity Insurance Company is for a maximum amount of $50,000. Each policy includes a pro rata clause. Due to defective electrical wiring, Tira's house catches fire and burns completely. The value of the house at the time of the loss is $120,000. Tira files a proof of loss with each insurer. What is an open policy? What is a pro rata clause? What is the liability of Unity and Verity for this event?