Pls answer my previous questions.

I really, really, really need help!

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

Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?

Find the solution of each of the following.