What is the benchmark fraction of 7/10 x 16

What is a possible solutions of the x> 3?

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

Two variables, x and y, vary inversely, and x=12 when y=4. what is the value of y when x=3?