An equation is shown below: 6(2x - 11) + 15 = 3x + 12
What value of x makes the equation true? HELP

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

We just started the introduction into circles and i have no idea how to do this.

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?