There are 9 books stacked on a shelf. the thickness of each book is either 1 inch or 2 inches. the height of the stack of 9 books is 14 inches. which system of equations can be used to determine x, the number of 1-inch-thick books in the stack, and y, the number of 2-inch-thick books?

a.) x + y = 14 2x + y = 9

b.) x + y = 14 x + 2y = 9

c.) x + y = 9 x + 2y = 14

d.) x + y = 9 2x + y = 14

What is the celsius temperature that is equal to 94 degrees fahrenheit using the formula f=9/5 c+32

Find the number of real number solutions for the equation. x2 + 5x + 7 = 0 0 cannot be determined 1 2

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling