For this case we have the following expression:

We must find the value of the expression when:

Substituting we have:

Finally, the value of the expression is:

ANswer:

A= 1/2(7 + 11)(5)
A = 1/2(18)(5)
A = 45 square units
Without the original equation, it's impossible to answer that question. I'm sorry.
Louise needs 8 ounces of chopped onions to serve 25 people