I can’t get this answer right

What is the area of triangle abc if a = 8, b = 11, and c = 15?

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.

Acomputer store bought a program at a cost of $10 and sold it for $13. find the percent markup