Answer: 80
Step-by-step explanation: When rounding to the nearest 10, you need to examine the number you are trying to round. If the number has a 1's place that is 4 or lower, you round to 70, but if the 1's position is 5 to 9, you round to 80. In this case, 77 can be rounded to 80, since the 1's place number is between 5 and 9.
Hope this helps! :)