What are some ways unit rates are useful

What is the rate of change of a line that passes through (2,-5) and (6,-2)?

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.

Determine which expressions represent real numbers and which expressions represent complex number. asaaap! plis!