What is the measure of an angle corresponding to 89?
It’s for a test please quickly help

What is the standard deviation of the following data set rounded to the nearest tenth? 3, 17, 18, 15, 12, 21, 9

Can someone check if i did this correct. it’s number 4 if you’re wondering.

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?