Normally, you would just use a calculator and enter √80. But if you don't want to use a calculator, remember that the square root is the number that goes into something when multiplied by itself. For example, √9 is 3, because 3*3=9. So, 80 is very close to 81. √81=9. Therefore, the answer to √80 will be slightly smaller than and extremely close to 9. Therefore, the answer is B) 8.9
Hope this helped! Comment if you have any questions.