阅读短文，回答问题。

    Hello. I'm Peter. I'm a pupil. I go to school and study the boring knowledge(知识) every day now. I hope our school will change in the future. Schools will be different then. They will be under the sea, on high mountains and even in space. Robots will help us find books in the library and do our homework at home. We will use computers in all our lessons. They will help us see dinosaurs and other interesting things. We will have lessons with students from other countries. We will do a lot of things online together. We won't carry books to school. All our books will be on a small computer.

在三角形中，∠ 1＝42°，∠ 2＝38°，求∠ 3的读数。