Could someone check over my answer, you.

1/3(x-10)=-4 solve for x with steps

What is the value of x when x + 7 = 21?

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?