Solving systems of equations by substitution -2x-3(6-11)=-7

The head librarian at the library of congress has asked her assistant for an interval estimate of the mean number of books checked out each day. the assistant provides the following interval estimate: from 740 to 920 books per day. what is an efficient, unbiased point estimate of the number of books checked out each day at the library of congress?

Acircle has a circumference of 28.36 units what is the diameter of the circle

Two times a number plus three times another number equals 4. three times the first number plus four times the other number is 7. find the numbers