Natasha went to Paris for a spring holiday. Because May is normally a very rainy month, Natasha did not make any arrangements for watering her garden. In fact, it did not rain at all during May. Her neighbour, Vlado, watered her garden because he knew that Natasha would not want her plants to die. When Natasha returned from her holiday and found out that Vlado had saved her garden, she thanked Vlado and promised to pay him $200 for his time and effort. Vlado immediately went to the gardening store and spent $200 on gardening supplies. When Vlado subsequently asked for the $200 that Natasha had promised, she refused to pay Vlado