How do I solve a system of equation? Can someone explain it to me?

For example:

x - y = 4

2x + y = 5

The time required for a citizen to complete the 2010 u. s. census "long" form is normally distributed with a mean of 40 minutes and a standard deviation of 10 minutes.

What number can replace the n in n/12 to make it equivalent to 1/2? 6 8 9 10

120 meters of fence are available to build a rectangular pen that is also divided in half by a fence. Let the width of this pen be x. Express the total area of the pen in terms of x and find the value of x for the greatest total area.

8 (8-6v) is equaled to

Kim needs to place 32 mystery books and 56 biography books on library shelves. She is to place the maximum number of books on each shelf so that all the shelves have the same number of books. Each shelf will contain only one type of book.

What is the sum of the first 7 terms of the series - 8 + 16 - 32 + 64 - ... ? Enter your answer in the box.

What is the nearest ten and hundred 622

1/6 (k-9) = 4 what does k equal

A pen has a mass of 46 grams. A bannana has a mass that is 83 grams more then a pen. what is the mass of the bannana in grams.

Find all solutions of the given system of equations and check your answer graphically. hint [see examples 1-4.] (if there is no solution, enter no solution. if the system is dependent, express your answer in terms of x, where y = y (x).