Read the passage and choose the best answer to each of the following questions.

An earthquake measuring 7.8 on the Richter scale hit Nepal on April 25th, 2015. It was the most powerful earthquake to strike Nepal since 1934. The earthquake occurred in central Nepal. It also affected India, Bangladesh and Tibet, China. The earthquake killed more than 8,800 people and injured over 23,000 people. Hundreds of thousands of people were made homeless with entire villages flattened. Kathmandu Burbar Square, a UNESCO World Heritage Site, was destroyed. The earthquake also caused an avalanche on Mount Everest which killed at least 19 people. About 90% of soldiers from Nepalese Army were sent to stricken areas. Many countries and international organizations sent medical experts, emergency workers, rescue staff, and money as well as providing medical supplies, food and equipment to help Nepal.

How many countries are affected by the earthquake?