Need help with this please if anyone knows :)

Acircle has a diameter will endpoints of (-2,8) and (6, 4). what is the center of the circle

The brain volumes (cm cubed) of 50 brains vary from a low of 904 cm cubed to a high of 1488 cm cubed. use the range rule of thumb to estimate the standard deviation s and compare the result to the exact standard deviation of 175.5 cm cubed, assuming the estimate is accurate if it is within 15 cm cubed

Angles r and s are complementary. the measure of angle r is 31 degrees. which equation can be used to find angle s?