I need this question ASAP about triangles

How do i do this activity, is appreciated

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

3x + 4y = 5 x- 3y = -7 solve by substitution