Explain how use mental math in 17+38

Liz is shipping a package to her friend. the maximum weight of a medium flat-rate box is 20 pounds, including the box which weighs 6 ounces. write and solve an inequality to describe the possible weight ,w, of the contents that liz will ship to her friend if she must use a medium flat-rate box.

Don't know how to find x given these segment lengths

Askateboard ramp is in the shape of a right triangle what is the height of the ramp