An 18-ounce jar of the sandwich spread will have a total of 2273 calories and 150 grams of fat. Write and solve a system of equations to find the number of ounces of peanut butter, grape jelly, and granola in each jar.
x + y + z = 18
168 x + 71 y + 132 z = 2273
14 x + 12 z = 150